Small clap adjustments

[tranzystorekk]

What does this PR do

Noticed that the --help output and generated manpage use uppercased Topgrade, which is inconsistent and potentially confusing to users. This PR fixes that, and additionally restyles clap keywords.

Standards checklist

• [x] The PR title is descriptive.
• [x] I have read CONTRIBUTING.md
• [x] Optional: I have tested the code myself