Adding cascading secrets to Deployment settings

[IaroslavTitov]

Summary

• Fixes: DeploymentSettings doesn't handle EnvironmentVariables if it's a secret and fails/ignore silently #447 (kinda)
• The reason secret was failing to create is due to this c# specific bug - [sdk/dotnet] Input<T> eagerly converts values to Output<T> leading to undesirable preview diffs pulumi-dotnet#22
• A secret among env vars made the whole object secret and it was skipped
• Recent change Adding support for secrets in all values in DeploymentSettings #467 actually made the issue worse - it is creating the env vars, but NOT secret (Thankfully I never released after that PR! 😅 )
• This PR adds cascading logic to envVars and username values - they are the only ones that are optionally secret

Testing

• Manual test

[github-actions]

Does the PR have any schema changes?

Looking good! No breaking changes found.
No new resources/functions.

Maintainer note: consult the runbook for dealing with any breaking changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (49003fc) to head (fc87d1c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #475   +/-   ##
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[pulumi-bot]

This PR has been shipped in release v0.27.4.