[Core feature] Plugin mode for flyteadmin server middleware

[katrogan]

Motivation: Why do you think this is important?

To permit flexibility in flyteadmin serving, such as custom authentication/audit logging middleware, authorization hooks and more, it would be useful to introduce a plugin system for hooking into flyteadmin service gRPC middleware

Goal: What should the final outcome look like, ideally?

End users should have the option to extend flyteadmin with their own middleware if their complex deployments require it

Describe alternatives you've considered

Checking in a finite set of middleware into flyteadmin code, using config flags to switch on or off.

Propose: Link/Inline OR Additional context

No response

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes