* docs: drop table of contents for `vmctl`
We already have it autogenerated on .github.io, so no need to keep it.
* docs: mention OpenTSDB migration feature for vmctl
* docs: sync docs for `vmalert`
The major change is adding `sort` directive to docs. For those docs which are copied
from internal packages `sort` is added via makefile command. For the rest it is added
manually since they're updated manually as well.
The rest of changes is connected with markdown formatting. For example, changing headers
in some files (`##` => `#`) makes navigation on .github.io to look better. This especially
useful for `changelog` docs.
Table of contents for `vmctl` is dropped, since we already have it autogenerated on .github.io.
No link changes expected. The corresponding PR to `cluster` branch will be made in follow-up PR.
It is better developing vmctl tool in VictoriaMetrics repository, so it could be released
together with the rest of vmutils tools such as vmalert, vmagent, vmbackup, vmrestore and vmauth.
