feat: add caption in file blocks

[brd6]

Description

Add caption property in the file blocks.

Motivation and context

Captions property are not available in the Video and Image blocks.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

PR checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 44.44444% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 51.31%. Comparing base (add38da) to head (ca47bf6).

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Additional details and impacted files

@@             Coverage Diff              @@
##               main      #37      +/-   ##
============================================
- Coverage     51.34%   51.31%   -0.03%     
- Complexity     1005     1008       +3     
============================================
  Files           216      216              
  Lines          2723     2732       +9     
============================================
+ Hits           1398     1402       +4     
- Misses         1325     1330       +5     

Files	Coverage Δ
src/RequestParameters.php	100.00% <ø> (ø)
src/Resource/AbstractResource.php	85.71% <ø> (ø)
src/Resource/Block/AbstractBlock.php	67.90% <ø> (ø)
src/Resource/RichText/AbstractRichText.php	63.63% <ø> (ø)
src/Resource/File/AbstractFile.php	69.23% <44.44%> (-7.44%)	⬇️