Add Resource modifiers docs / site

[anshulahuja98]

Thank you for contributing to Velero!

Please add a summary of your change

Does your change fix a particular issue?

Docs for : #6452

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[codecov-commenter]

Codecov Report

Merging #6501 (9805f87) into main (9c8275e) will decrease coverage by 0.18%.
Report is 8 commits behind head on main.
The diff coverage is n/a.

❗ Current head 9805f87 differs from pull request most recent head 94d3494. Consider uploading reports for the commit 94d3494 to get more accurate results

@@            Coverage Diff             @@
##             main    #6501      +/-   ##
==========================================
- Coverage   60.36%   60.18%   -0.18%     
==========================================
  Files         239      241       +2     
  Lines       25498    25617     +119     
==========================================
+ Hits        15391    15417      +26     
- Misses       9036     9130      +94     
+ Partials     1071     1070       -1     

see 5 files with indirect coverage changes

[anshulahuja98]

/kind changelog-not-required

[sseago]

A couple minor suggestions on wording, otherwise looks good.

[anshulahuja98]

A couple minor suggestions on wording, otherwise looks good.

Resolved the comments

[anshulahuja98]

@blackpiglet / @ywk253100 can you please review.