feat: Try to fallback to access token from CLI config file

[ErwinSteffens]

🔧 Changes

Fallback to access token from $HOME/.config/auth0/config.json for the given tenant.

When Keyring is not supported by the CLI (saving fails) the access token (without refresh token) is saved in the configuration file. Loading this token is not yet supported by Terraform provider.

📚 References

• Fallback to CLI access token from config file #1380
• Auth0 CLI for keeping access token in config when saving fails is here.

🔬 Testing

• I have tested loading the access token from my config file on my Macbook.
• Refactored the config loading to make testing easier.

📝 Checklist

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.47107% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.78%. Comparing base (62b13c9) to head (5d83479).

Files with missing lines	Patch %	Lines
internal/config/config.go	83.47%	15 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1381      +/-   ##
==========================================
+ Coverage   87.55%   87.78%   +0.22%     
==========================================
  Files         156      156              
  Lines       21888    21924      +36     
==========================================
+ Hits        19165    19245      +80     
+ Misses       2026     1973      -53     
- Partials      697      706       +9     

Files with missing lines	Coverage Δ
internal/provider/provider.go	98.85% <ø> (ø)
internal/config/config.go	79.80% <83.47%> (+19.27%)	⬆️

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[duedares-rvj]

@ErwinSteffens Hello 👋
Thanks again for this contribution. I tried to rebase this with main and resolve the conflicts. It seems I dont have write access.
Could you either rebase or provide me write permissions?
We shall merge this then :)

[duedares-rvj]

@ErwinSteffens 👋
Quick wave in case you missed the earlier comment :)

[ErwinSteffens]

@duedares-rvj You should have access now.

[ErwinSteffens]

@duedares-rvj I have update PR and fixed conflicts btw.