Rate-Limiter/Throtteling Concurrency

[fritterhoff]

Background

As discussed in #3294 we are stumbeling into some strange issues with to low rate limits. While we can mitigate these in our case by increasing the limits it is foreseeable that other service providers won't provide this option(s).

Idea

Either introduce a global limit of concurrency using a flag or provide an option to limit the concurrency per provider.