Add trace log message when failing to find Env Var

[SimonWahlin]

Fixes #13100

If verbose is set to true in bicepconfig.json, bicep now logs the names of all available environment variables when function readEnvironmentVariable fails to find the variable specified. This should hopefully help troubleshoot errors related to this function.

Example of output before:

Example of output after:

Contributing a feature

• I have opened a new issue for the proposal, or commented on an existing one, and ensured that the Bicep maintainers are good with the design of the feature being implemented
• I have included "Fixes #{issue_number}" in the PR description, so GitHub can link to the issue and close it when the PR is merged
• I have appropriate test coverage of my new feature

Microsoft Reviewers: Open in CodeFlow

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 7.71%. Comparing base (108d816) to head (0b1fc10).
Report is 363 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #13777       +/-   ##
===========================================
- Coverage   94.28%    7.71%   -86.57%     
===========================================
  Files        1113        7     -1106     
  Lines      100791      350   -100441     
  Branches     8734      127     -8607     
===========================================
- Hits        95028       27    -95001     
+ Misses       4595      322     -4273     
+ Partials     1168        1     -1167     

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see 1105 files with indirect coverage changes

[SimonWahlin]

@StephenWeatherford I see that one test is failing, but I don't really understand why, don't think it is related to the changes made. Can you help me run it again?