refactor(docs): generate documentation with Material for MkDocs

[kangasta]

Remove previous Jekyll based GitHub pages and replace those with MkDocs based solution that uses Material for MkDocs theme with few custom overrides. Remove generated documentation from main branch.

In addition, add custom logic for markdown command reference generation in order to:

• list command aliases in markdown files,
• present command options in tables for increased accessibility,
• display only long or short command description similarly than in --help outputs,
• and use *cobra.Command instead of output filename as input to file prefix function.

[kangasta]

To test the docs output:

git fetch
git checkout gh-pages
python3 -m http.server 8000 # or any other command that starts static HTTP server

or checkout this branch, run make docs and mkdocs serve.

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TODO After merge:

• Update GitHub pages settings to use gh-pages branch as is instead of Jekyll from main
• Add link to GitHub pages to repository website setting

[kangasta]

Good catch! I'll update Documentation section in README before merging this