[doc] OBJ resource usage

[bcm820]

What type of PR is this?
/kind documentation

What this PR does / why we need it:
Adds documentation for LinodeObjectStorageBucket resources.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

[amold1]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.08%. Comparing base (60f6c60) to head (9540fa6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
- Coverage   42.18%   42.08%   -0.10%     
==========================================
  Files          25       25              
  Lines        1356     1371      +15     
==========================================
+ Hits          572      577       +5     
- Misses        773      781       +8     
- Partials       11       13       +2     

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