Add improved CLI interface for removing remote media

[Gargron]

./bin/tootctl media remove --days 7 --background

Make the old rake task point to it. Benefits: It lets you choose whether to process files sequentially, or in background.

Fix #8187

[ClearlyClaire]

I'm not sure about adding yet another interface.
On the other hand, allowing people to run this task sequentially rather than using a queue is good, although the impact should be limited if said queue is really the lowest-priority one.

[Gargron]

@ThibG I intend to fully remove the rake interface, but feeling some pressure to release 2.5 soon, I don't feel like I have the time to rewrite everything at once.

The problem with rake is the argument system. To use any kind of arguments for commands, I have to either use rake's insane syntax (rake task['arg1', 'arg2']), or initialize my own option parser but have it only work with -- separating the rake part from the options part, and the code for that is getting very messy (mastodon.rake is very large).

With this new interface, I can split it into multiple, organized files, and the options and arguments handling is built in.

[mayaeh]

I think that ".to_i" is requires for "['NUM_DAYS']".

However, I still feel that it is not working properly.

I executed next line.
RAILS_ENV=production NUM_DAYS=60 bundle exec rake mastodon:media:remove_remote

After that, when I executed next line, multiple jobs were added to Sidekiq.
RAILS_ENV=production bundle exec bin/tootctl media remove --days 60 --background