External variables can override Devfile variables

[feloy]

What does this PR do?:

This PR adds an ExternalVariables option to the ParserArgs structure, to be able to override variables defined in the devfile with other values when parsing a Devfile.

Which issue(s) this PR fixes:

redhat-developer/odo#5489

PR acceptance criteria:

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Open new test/doc issues under the devfile/api repo
• Check each criteria if:
• There is a separate tracking issue. Add the issue link under the criteria
  or
• test/doc updates are made as part of this PR
• If unchecked, explain why it's not needed

• Unit/Functional tests

• QE Integration test

• Documentation

• Client Impact

How to test changes / Special notes to the reviewer:

[yangcao77]

Do you mind adding a unit test case for the ExternalVariables?

[feloy]

Do you mind adding a unit test case for the ExternalVariables?

Sure, I'll add a unit test case

[yangcao77]

changes look good to me

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: feloy, yangcao77

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• OWNERS [yangcao77]

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