Add API for setting task queue rate limiting

[lorensr]

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

A user wants to dynamically change maxTaskQueueActivitiesPerSecond. Currently, in order to do so, they need to redeploy all Workers that are on that queue:

Describe the solution you'd like

A gRPC method for setting a new value (takes task queue name and a number). Then a user can not set it on the Workers, and only use gRPC/tctl/SDK.