Make enviroment variable tracking external SDK into a constant

[davidmrdavid]

This PR is a follow up to #839

In it, we introduced a new optional environment variable named ExternalDurablePowerShellSDK. This environment variable controls whether the external DF SDK logic is invoked.

In this PR, we turn that variable name into a constant string, for re-usability and logging. No logic changes have taken place other than logging the variable name in usage warnings.

Issue describing the changes in this PR

resolves N/A

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Additional PR information

[Francisco-Gamino]

LGTM. Please add a test case if you do not already have one for this scenario. Thank you.

[davidmrdavid]

Thanks @Francisco-Gamino. The use of this environment variable has been tested in this several times. We mock it's contents everytime we mock the result of "isExternalDurableSdkLoaded".

Does that meet your request?

[Francisco-Gamino]

Thanks @Francisco-Gamino. The use of this environment variable has been tested in this several times. We mock it's contents everytime we mock the result of "isExternalDurableSdkLoaded".

Does that meet your request?

Thank you @davidmrdavid for the follow up. Do we have a test case that validates the expected log statement when the feature flag is enabled?

azure-functions-powershell-worker/src/DurableWorker/DurableController.cs

Line 84 in 4c12426

_logger.Log(isUserOnlyLog: false, LogLevel.Error, String.Format(PowerShellWorkerStrings.PotentialDurableSDKClash, Utils.ExternalDurableSdkName, Utils.ExternalDurableSdkEnvVariable));

[davidmrdavid]

@Francisco-Gamino. Ah, not for the log itself. I'll look to add that.

[davidmrdavid]

As discussed, tracked here: #910