Use setup-codeql logic for finding release assets in start-proxy

[mbg]

The start-proxy Action currently uses its own getReleaseByVersion function to get hold of the release that we expect to find the proxy assets at. That function has hard-coded owner and repo values for the default github/codeql-action repository. This repository may not be available in all environments. In such environments, getReleaseByVersion fails and we fall-back to the hard-coded release obtained from getFallbackUrl instead.

Broadly, this PR does the following:

• getCodeQLActionRepository and getCodeQLBundleDownloadURL are refactored out of setup-codeql into a new setup/repository module.
• We then use getCodeQLAssetDownloadURL (renamed from getCodeQLBundleDownloadURL) in the start-proxy action to apply the same logic for finding a suitable release as used by setup-codeql.
• The hard-coded fallback has been removed. The default URL returned by getCodeQLBundleDownloadURL is essentially equivalent, except that it uses the linked version rather than a hard-coded one. We have been shipping proxy artifacts successfully with releases for a good while now, so the fallback shouldn't be needed anymore.

There are some drive-by improvements to logging and assertions for sinon stubs.

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Which use cases does this change impact?

Workflow types:

• Managed - Impacts users with dynamic workflows (Default Setup, Code Quality, ...).

Products:

• Code Scanning - The changes impact analyses when analysis-kinds: code-scanning.
• Code Quality - The changes impact analyses when analysis-kinds: code-quality.
• Other first-party - The changes impact other first-party analyses.

Environments:

• Dotcom - Impacts CodeQL workflows on github.com and/or GitHub Enterprise Cloud with Data Residency.
• GHES - Impacts CodeQL workflows on GitHub Enterprise Server.

How did/will you validate this change?

• Unit tests - I am depending on unit test coverage (i.e. tests in .test.ts files).
• End-to-end tests - I am depending on PR checks (i.e. tests in pr-checks).

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Rollback - Change can only be disabled by rolling back the release or releasing a new version with a fix.

How will you know if something goes wrong after this change is released?

• Telemetry - I rely on existing telemetry or have made changes to the telemetry.
  • Dashboards - I will watch relevant dashboards for issues after the release. Consider whether this requires this change to be released at a particular time rather than as part of a regular release.
  • Alerts - New or existing monitors will trip if something goes wrong with this change.

Are there any special considerations for merging or releasing this change?

• No special considerations - This change can be merged at any time.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.