Pause individual partitions separately

[npepinpe]

Is your feature request related to a problem? Please describe.

We had an incident where we needed to pause partitions, which works great, but we only wanted to pause a single one. When you pause all partitions, it can then create problems on others which may be healthy/fine unnecessarily.

Describe the solution you'd like

I'd like to be able to not only pause all partitions, but also pause partitions individually, where I can do:

• curl -XPOST http://localhost:9600/actuator/partitions/1/pauseProcessing
• curl -XPOST http://localhost:9600/actuator/partitions/1/resumeProcessing
• curl -XPOST http://localhost:9600/actuator/partitions/1/pauseExporting
• curl -XPOST http://localhost:9600/actuator/partitions/1/resumeExporting

Describe alternatives you've considered

We can carefully rebalance the cluster until we have a node which is leader for only the partition we want to pause, but that's brittle and time consuming.

Additional context

https://docs.google.com/document/d/1EsGS-SXGLf1iInHLmCr0saQBLlxz1o5DYjpy5Q50wmQ/

[menski]

we should reevaluate after #9996 was scoped and maybe implemented

[Zelldon]

This would also be interesting for chaos experiments.