chore: Enable resource policy tests with SA credentials

[lantoli]

Description

Enable resource policy tests with SA credentials.

Link to any related issue(s): CLOUDP-350334

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR. A migration guide must be created or updated if the new feature will go in a major version.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR. A migration guide must be created or updated.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contributing guides
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals I have added appropriate changelog entries.
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Further comments

[Copilot]

Pull Request Overview

This PR enables resource policy tests to use service account (SA) credentials as an alternative to API key authentication. The change adds support for client ID and secret authentication alongside existing public/private key authentication for resource policy testing.

• Adds new service account credential inputs to the GitHub Actions workflow
• Updates the test runner to conditionally use either API keys or service account credentials based on the use_sa parameter
• Maintains backward compatibility with existing API key authentication

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/acceptance-tests.yml	Adds service account client ID and secret inputs for resource policy tests
.github/workflows/acceptance-tests-runner.yml	Updates workflow to conditionally use SA credentials and adds new required inputs

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