Prioritize UI/tctl when system is throttled

[pdoerner]

What changed?

• Added a new possible value for the caller-type header: operator
• This header should be set by web UI and tctl to indicate that requests should be given higher precedence
• Rate limiters for persistence, history, matching, and visibility were updated with a new priority corresponding to operator requests
• These new priorities have a lower RPS limit to prevent abusing the header to get high priority for all requests. Currently the operator priority is allowed 20% of the rate of the existing rate limiters

Why?
When the system is being throttled, users would like to be able to debug using the web UI and/or tctl without running into rate limit errors

How did you test it?
New unit tests

Potential risks
The operator RPS is set too low leading to new rate limit errors

Is hotfix candidate?
No

[yycptt]

Can you double check if visibility persistence client has any rate limiter? If so that probably should also be updated.

[yycptt]

Overall LGTM. Please land after addressing the comments.