[PoP token Cache] Fallback to no caching when encrypted cache creation fails

[vineeth-thumma]

Fallback to no caching when encrypted caching initialization fails due to reasons like restricted kernel keyring access, etc.

• Only initialize PoP cache explicitly when the pop flag is set
• Fallback to not use pop token caching when pop cache initialization fails
• Proactively test storage capability before creating the cache
  Reference: https://github.com/Azure/azure-sdk-for-go/blob/main/sdk/azidentity/cache/cache.go
• Implement PoPKeyProvider interface

Relevant WI: https://msazure.visualstudio.com/AzureArcPlatform/_workitems/edit/35560158

[codecov-commenter]

Codecov Report

❌ Patch coverage is 54.00000% with 69 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.61%. Comparing base (15edb67) to head (54e4d35).
⚠️ Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/internal/pop/cache/cache.go	45.09%	21 Missing and 7 partials ⚠️
pkg/internal/pop/poptoken.go	0.00%	15 Missing ⚠️
pkg/internal/token/execCredentialPlugin.go	46.15%	6 Missing and 1 partial ⚠️
pkg/internal/token/options.go	66.66%	4 Missing and 1 partial ⚠️
pkg/internal/token/clientcertcredentialwithpop.go	75.00%	3 Missing ⚠️
...kg/internal/token/clientsecretcredentialwithpop.go	75.00%	3 Missing ⚠️
...ernal/token/interactivebrowsercredentialwithpop.go	72.72%	3 Missing ⚠️
...nternal/token/usernamepasswordcredentialwithpop.go	76.92%	3 Missing ⚠️
pkg/internal/token/provider.go	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #715      +/-   ##
==========================================
- Coverage   63.43%   55.61%   -7.83%     
==========================================
  Files          37       47      +10     
  Lines        2210     3057     +847     
==========================================
+ Hits         1402     1700     +298     
- Misses        733     1193     +460     
- Partials       75      164      +89     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.