Adding data source for App Connection resource

[palramanathan]

Data source for AppConnection resource

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

`google_beyondcorp_app_connection`

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I've detected that you're a community contributor. @melinath, a repository maintainer, has been assigned to assist you and help review your changes.

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 3 files changed, 270 insertions(+))
Terraform Beta: Diff ( 3 files changed, 270 insertions(+))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2374
Passed tests 2121
Skipped tests: 247
Failed tests: 6

Action taken

Triggering VCR tests in RECORDING mode for the tests that failed during VCR. Click here to see the failed tests

TestAccLoggingBucketConfigProject_cmekSettings|TestAccContainerCluster_withInvalidGatewayApiConfigChannel|TestAccDataSourceGoogleBeyondcorpAppConnection_optionalProject|TestAccDataSourceGoogleBeyondcorpAppConnection_basic|TestAccDataSourceGoogleBeyondcorpAppConnection_optionalRegion|TestAccDataSourceGoogleBeyondcorpAppConnection_optionalProjectRegion

[modular-magician]

Tests passed during RECORDING mode:
TestAccLoggingBucketConfigProject_cmekSettings[Debug log]
TestAccContainerCluster_withInvalidGatewayApiConfigChannel[Debug log]
TestAccDataSourceGoogleBeyondcorpAppConnection_optionalProject[Debug log]
TestAccDataSourceGoogleBeyondcorpAppConnection_optionalRegion[Debug log]

Tests failed during RECORDING mode:
TestAccDataSourceGoogleBeyondcorpAppConnection_basic[Error message] [Debug log]
TestAccDataSourceGoogleBeyondcorpAppConnection_optionalProjectRegion[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 3 files changed, 270 insertions(+))
Terraform Beta: Diff ( 3 files changed, 270 insertions(+))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2375
Passed tests 2121
Skipped tests: 248
Failed tests: 6

Action taken

Triggering VCR tests in RECORDING mode for the tests that failed during VCR. Click here to see the failed tests

TestAccContainerCluster_withInvalidGatewayApiConfigChannel|TestAccBigtableAppProfile_bigtableAppProfileSingleclusterExample|TestAccBigtableAppProfile_bigtableAppProfileAnyclusterExample|TestAccDataSourceGoogleBeyondcorpAppConnection_basic|TestAccLoggingBucketConfigProject_cmekSettings|TestAccDataSourceGoogleBeyondcorpAppConnection_optionalProjectRegion

[modular-magician]

Tests passed during RECORDING mode:
TestAccContainerCluster_withInvalidGatewayApiConfigChannel[Debug log]
TestAccBigtableAppProfile_bigtableAppProfileSingleclusterExample[Debug log]
TestAccBigtableAppProfile_bigtableAppProfileAnyclusterExample[Debug log]
TestAccDataSourceGoogleBeyondcorpAppConnection_basic[Debug log]
TestAccLoggingBucketConfigProject_cmekSettings[Debug log]
TestAccDataSourceGoogleBeyondcorpAppConnection_optionalProjectRegion[Debug log]

All tests passed
View the build log or the debug log for each test

[melinath]

Rather than having tests for different combinations of project / region being set, please have a basic test and a "full" test, where the basic test sets the smallest number of fields possible and full test sets as many as possible.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 3 files changed, 160 insertions(+))
Terraform Beta: Diff ( 3 files changed, 160 insertions(+))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2380
Passed tests 2127
Skipped tests: 248
Failed tests: 5

Action taken

Triggering VCR tests in RECORDING mode for the tests that failed during VCR. Click here to see the failed tests

TestAccFirebaserulesRelease_BasicRelease|TestAccContainerCluster_withInvalidGatewayApiConfigChannel|TestAccBigQueryDataTable_bigtable|TestAccLoggingBucketConfigProject_cmekSettings|TestAccDataSourceGoogleBeyondcorpAppConnection_full

[modular-magician]

Tests passed during RECORDING mode:
TestAccFirebaserulesRelease_BasicRelease[Debug log]
TestAccContainerCluster_withInvalidGatewayApiConfigChannel[Debug log]
TestAccBigQueryDataTable_bigtable[Debug log]
TestAccLoggingBucketConfigProject_cmekSettings[Debug log]
TestAccDataSourceGoogleBeyondcorpAppConnection_full[Debug log]

All tests passed
View the build log or the debug log for each test

[palramanathan]

Thanks for the review @melinath. Updated the PR. Please review again.

[melinath]

LGTM