fix(CLI): add tool name to Retina CLI help message

[k-nzw]

Description

This PR fixes a bug where the tool name is missing in the help message of Retina CLI.
As a side effect, the kubectl-retina completion command will now generate a completion script that works correctly.

Related Issue

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#973

Checklist

• I have read the contributing documentation.
• I signed and signed-off the commits (git commit -S -s ...). See this documentation on signing commits.
• I have correctly attributed the author(s) of the code.
• I have tested the changes locally.
• I have followed the project's style guidelines.
• I have updated the documentation, if necessary.
• I have added tests, if applicable.

Screenshots (if applicable) or Testing Completed

Please add any relevant screenshots or GIFs to showcase the changes made.

Additional Notes

before:

$ kubectl-retina
Usage:
   [command]

after:

$ kubectl-retina
A kubectl plugin for Retina
Retina is an eBPF distributed networking observability tool for Kubernetes.

Usage:
  kubectl-retina [command]

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