Documentation: Unify man pages and manual documentation

[earboxer]

Is your feature request related to a problem? Please describe.

This repository ships outdated man pages inside the doc/ folder (they reference sphinx config locations, and haven't much been touched, save for copyright updates). These are largely redundant with relevant documentation in manual/.

Describe the solution you'd like

Delete outdated man files, and convert relevant pages in the manual to man-style pages, which can be converted by a tool like go-md2man

(e.g. I currently do this in Alpine Linux's packaging script: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/47533/diffs)

Describe alternatives you've considered

• Manually update the man pages to be more up to date (and try to be more vigilant about updating in both places)
• Delete the man pages and don't provide an alternative

Additional context

[sanikolaev]

The man pages have been updated in https://github.com/manticoresoftware/manticoresearch/commit/d3e1518d38de5ae5bff6e9f5336c23d7aafb7f2e and a few previous commits.