Document stream identification for rate-limit or validation errors

[dannykopping]

Is your feature request related to a problem? Please describe.
https://grafana.com/docs/loki/next/operations/request-validation-rate-limits/ describes all the rate-limit and validation errors that can occur, but it doesn't give advice in each case for how to identify the offending stream; this is essential for resolving the problem.

Describe the solution you'd like
Step-by-step guide to identify problematic streams

Some limit/error responses may not specify which streams were the offending ones, and in those cases we either need to log them (and document how to find these logs), or return them in the response.

Describe alternatives you've considered
N/A

Additional context
N/A