[7.x](backport #25219) Introduce httpcommon package in libbeat (add support for Proxy)

[mergify]

This is an automatic backport of pull request #25219 done by Mergify.
Cherry-pick of 4accfa8 has failed:

On branch mergify/bp/7.x/pr-25219
Your branch is up to date with 'origin/7.x'.

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Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   dev-tools/cmd/dashboards/export_dashboards.go
	modified:   filebeat/fileset/modules_integration_test.go
	modified:   filebeat/fileset/pipelines_test.go
	modified:   heartbeat/docs/monitors/monitor-http.asciidoc
	modified:   heartbeat/monitors/active/dialchain/tls.go
	modified:   heartbeat/monitors/active/http/config.go
	modified:   heartbeat/monitors/active/http/http.go
	modified:   heartbeat/monitors/active/http/http_test.go
	modified:   heartbeat/monitors/active/http/task.go
	modified:   libbeat/common/transport/client.go
	new file:   libbeat/common/transport/httpcommon/httpcommon.go
	new file:   libbeat/common/transport/httpcommon/proxy.go
	modified:   libbeat/common/transport/tls.go
	modified:   libbeat/common/transport/tlscommon/config.go
	modified:   libbeat/common/transport/tlscommon/server_config.go
	modified:   libbeat/common/transport/tlscommon/tls.go
	modified:   libbeat/common/transport/tlscommon/tls_config.go
	modified:   libbeat/common/transport/tlscommon/types.go
	modified:   libbeat/common/transport/transport.go
	modified:   libbeat/esleg/eslegclient/api_test.go
	modified:   libbeat/esleg/eslegclient/bulkapi_mock_test.go
	modified:   libbeat/esleg/eslegclient/config.go
	modified:   libbeat/esleg/eslegclient/connection.go
	modified:   libbeat/esleg/eslegclient/connection_integration_test.go
	modified:   libbeat/idxmgmt/ilm/client_handler_integration_test.go
	modified:   libbeat/kibana/client.go
	modified:   libbeat/kibana/client_config.go
	modified:   libbeat/licenser/elastic_fetcher_integration_test.go
	modified:   libbeat/licenser/elastic_fetcher_test.go
	modified:   libbeat/monitoring/report/elasticsearch/elasticsearch.go
	modified:   libbeat/outputs/elasticsearch/client.go
	modified:   libbeat/outputs/elasticsearch/client_proxy_test.go
	modified:   libbeat/outputs/elasticsearch/config.go
	modified:   libbeat/outputs/elasticsearch/docs/elasticsearch.asciidoc
	modified:   libbeat/outputs/elasticsearch/elasticsearch.go
	modified:   libbeat/outputs/logstash/logstash_integration_test.go
	modified:   libbeat/template/load_integration_test.go
	modified:   metricbeat/helper/config.go
	modified:   metricbeat/helper/http.go
	modified:   metricbeat/helper/http_test.go
	modified:   metricbeat/module/apache/status/status_test.go
	modified:   metricbeat/module/envoyproxy/server/server_test.go
	modified:   x-pack/elastic-agent/CHANGELOG.next.asciidoc
	modified:   x-pack/elastic-agent/pkg/agent/application/pipeline/stream/factory.go
	modified:   x-pack/elastic-agent/pkg/agent/application/upgrade/step_download.go
	modified:   x-pack/elastic-agent/pkg/agent/cmd/container.go
	modified:   x-pack/elastic-agent/pkg/agent/cmd/enroll_cmd.go
	modified:   x-pack/elastic-agent/pkg/artifact/config.go
	modified:   x-pack/elastic-agent/pkg/artifact/download/fs/verifier_test.go
	modified:   x-pack/elastic-agent/pkg/artifact/download/http/downloader.go
	modified:   x-pack/elastic-agent/pkg/artifact/download/http/elastic_test.go
	modified:   x-pack/elastic-agent/pkg/artifact/download/http/verifier.go
	modified:   x-pack/elastic-agent/pkg/artifact/download/localremote/downloader.go
	modified:   x-pack/elastic-agent/pkg/artifact/download/snapshot/downloader.go
	modified:   x-pack/elastic-agent/pkg/remote/client.go
	modified:   x-pack/elastic-agent/pkg/remote/config.go
	modified:   x-pack/elastic-agent/pkg/remote/config_test.go
	modified:   x-pack/filebeat/input/httpjson/config.go
	modified:   x-pack/filebeat/input/httpjson/input.go
	modified:   x-pack/filebeat/input/httpjson/input_cursor.go
	modified:   x-pack/filebeat/input/httpjson/input_stateless.go
	modified:   x-pack/filebeat/input/httpjson/input_test.go
	modified:   x-pack/filebeat/input/httpjson/internal/v2/config.go
	modified:   x-pack/filebeat/input/httpjson/internal/v2/config_request.go
	modified:   x-pack/filebeat/input/httpjson/internal/v2/input.go
	modified:   x-pack/filebeat/input/httpjson/internal/v2/input_cursor.go
	modified:   x-pack/filebeat/input/httpjson/internal/v2/input_stateless.go
	modified:   x-pack/filebeat/input/httpjson/internal/v2/request_test.go
	modified:   x-pack/libbeat/common/cloudfoundry/config.go
	modified:   x-pack/libbeat/common/cloudfoundry/hub.go
	modified:   x-pack/metricbeat/module/openmetrics/collector/_meta/data.json
	modified:   x-pack/metricbeat/module/prometheus/collector/_meta/data.json

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   libbeat/monitoring/report/elasticsearch/config.go
	both modified:   metricbeat/module/elasticsearch/index/data_test.go

To fix up this pull request, you can check it out locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

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• Build Cause: Pull request #26587 updated

• Start Time: 2021-06-30T14:58:41.845+0000

• Duration: 157 min 29 sec

• Commit: 1fe09d6

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Test	Results
Failed	0
Passed	47835
Skipped	5291
Total	53126

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Test stats 🧪

Test	Results
Failed	0
Passed	47835
Skipped	5291
Total	53126

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b mergify/bp/7.x/pr-25219 upstream/mergify/bp/7.x/pr-25219
git merge upstream/7.x
git push upstream mergify/bp/7.x/pr-25219