feat: Add examples to --help output for "gpg add"

[Ratangulati]

Created another issue for the issue #15690. #L109

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• Optional. My organization is added to USERS.md.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (9e0e8d5) 49.62% compared to head (60ecf32) 49.60%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #16020      +/-   ##
==========================================
- Coverage   49.62%   49.60%   -0.02%     
==========================================
  Files         267      267              
  Lines       46479    46484       +5     
==========================================
- Hits        23063    23058       -5     
- Misses      21144    21153       +9     
- Partials     2272     2273       +1     

Files	Coverage Δ
cmd/argocd/commands/gpg.go	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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[crenshaw-dev]

Thanks, @Ratangulati!