[Messenger] Add a scheduler component

[fabpot]

Q	A
Feature PR	symfony/symfony#47112
PR author(s)	@upyx, @fabpot
Merged in	6.3

We created this issue to not forget to document this new feature. We would really appreciate if you can help us with this task. If you are not sure how to do it, please ask us and we will help you.

To fix this issue, please create a PR against the 6.3 branch in the symfony-docs repository.

Thank you! 😄

[alexandre-daubois]

Let's close this one also?

[javiereguiluz]

There's still many work to do to fully document this component, but the initial docs are now read. Let's close it as fixed. Thanks for checking this Alex.