This reverts merge request !2824

Includes a new mix task: pleroma.database fill_old_hashtags

- start oban in mix tasks with empty queues, plugins and crontab
- fix for update_users_following_followers_counts
- fix for removed logo.png
- typo in resend confirmation emails mix task docs
- fix for uploads mix task (start Majic.Pool)
- fix for creating user mix task (start :fast_html app)

Bunch of reorganization and consolidation

While taking a final look at instance.gen before releasing I noticed
that the release_env task outputs messages in broken english. Upon
further inspection it seems to have even more severe issues which, in
my opinion, warrant it's at least temporary removal:
- We do not explain what it actually does, anywhere. Neither the task
 docs nor instance.gen, nor installation instructions.
- It does not respect FHS on OTP releases (uses /opt/pleroma/config even
 though we store the config in /etc/pleroma/config.exs).
- It doesn't work on OTP releases, which is the main reason it exists.
Neither systemd nor openrc service files for OTP include it.
- It is not mentioned in install guides other than the ones for Debian
and OTP releases.

Since python doesn't have a way to lock deps for a particlar project
by default, I didn't bother with it. This resulted in mkdocs updating at
some point, bringing a breaking change to how tabs are declared and
broken tabs on docs-develop.pleroma.social. I've learned my lesson
and locked deps with pipenv in pleroma/docs!5. This MR updates Pleroma
docs to use the new tab style, fortunately my editor did most of it.

Closes #2045

This reverts merge request !2763

* It was still written for From Source installs. Now it's both OTP and From Source
* I linked to the cheatsheet where it was about configuration
* I moved the mix tasks of the robot.txt section to the CLI tasks and linked to it
    * i checked the code at https://git.pleroma.social/pleroma/pleroma/-/blob/develop/lib/mix/tasks/pleroma/robotstxt.ex and it doesn't seem to more than just this one command with this option
* I also added the location of robot.txt and an example to dissallow everything, but allow the fediverse.network crawlers
* The Thumbnail section still linked to distsn.org which doesn't exist any more. I changed it to a general statemant that it can be used by external applications. (I don't know any that actually use it.)
* Both the logo and TOS need an extra `static` folder. I've seen confusion about that in #pleroma so I added an Important note.

Co-authored-by: Roman Chvanikov <chvanikoff@pm.me>

Not useful for source releases as we don't have a way to automate connecting to the running instance.