Add support for configuring scheduler migration timeout

[Sovietaced]

We recently upgrade Armada and the scheduler migration timed out with the default 5 minute timeout. It would be nice if this timeout could be made configurable.

[dejanzele]

I plan to create a better support for migrations, I'll write up my proposal in a new Issue.

When applying migrations, ideally, ingesters should be stopped, so I'd like to handle that scenario also.