feat: all backends support making them as read-only

[AJIOB]

For the local developers we want to provide the access to the remote cache server in read-only mode.

So, this PR allows read-only access to read-write storages via per-storage specific flag

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.57658% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.34%. Comparing base (8825b4a) to head (aab1fa8).

Files with missing lines	Patch %	Lines
src/config.rs	75.00%	15 Missing ⚠️
src/cache/cache.rs	78.43%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2705      +/-   ##
==========================================
- Coverage   74.41%   74.34%   -0.07%     
==========================================
  Files          70       70              
  Lines       39211    39460     +249     
==========================================
+ Hits        29177    29337     +160     
- Misses      10034    10123      +89     

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