Support fairness across clients of a receiver

[mx-psi]

Copying from the original thread:

I have two SDKs writing to the collector. If one is super chatty, can I prevent it from overwhelming the pipeline and "hiding" the data from the other SDK?

and another example (which may not be solvable with the same solution, but is illustrative of the general issue):

I have two file log receivers configured. One is pulling "audit/access" logs the other general logs. Can I ensure that a surge in general logs does NOT interfere with the access-log pipeline (and vice-versa)? How would I do that?

This may be implementable via #7441

Additional context: Part of the discussion in #11499, see https://docs.google.com/document/d/1BO7hMg0K7zFQ0219z61yRj-2JMMTW_HfoX3Vt6kXW8E/edit?disco=AAABU_a4M-E. This relates to #8632 and #7441