Add oras command to generate docs

[TerryHowe]

What this PR does / why we need it: Add oras command to generate docs

This would replace the janky script I wrote for the docs site. Partial example:

## oras blob delete
      
Delete a blob from a remote registry

### Synopsis
      
Delete a blob from a remote registry               
      
Example - Delete a blob:                           
  oras blob delete localhost:5000/hello@sha256:9a201d228ebd966211f7d1131be19f152be428bd373a92071c71d8deaf83b3e5

Example - Delete a blob without prompting confirmation:
  oras blob delete --force localhost:5000/hello@sha256:9a201d228ebd966211f7d1131be19f152be428bd373a92071c71d8deaf83b3e5
... 

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 #

Please check the following list:

• [x] Does the affected code have corresponding tests, e.g. unit test, E2E test?
• [ ] Does this change require a documentation update?
• [ ] Does this introduce breaking changes that would require an announcement or bumping the major version?
• [ ] Do all new files have an appropriate license header?

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 87.42%. Comparing base (7ab61a4) to head (cd7d8c7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1894      +/-   ##
==========================================
+ Coverage   87.29%   87.42%   +0.12%     
==========================================
  Files         143      144       +1     
  Lines        5535     5589      +54     
==========================================
+ Hits         4832     4886      +54     
  Misses        417      417              
  Partials      286      286              

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[TerryHowe]

It would be hard to add more coverage and I'm not sure how codecov/patch is calculating this:

oras.land/oras/cmd/oras/root/docs.go:45:						docsCmd				90.9%
oras.land/oras/cmd/oras/root/docs.go:71:						run				85.2%