generator: consider converting repeated fields to HTTP query parameters

Currently, we skip repeated fields found in proto request messages when formatting query parameters for GET requests. This may or may not be correct and needs some investigation.

Start by locating the generator code that formats query parameters for GET requests and trace how repeated fields in proto request messages are handled. Investigate whether repeated fields should be converted, then document the decision and validate it with the relevant generator tests; the issue does not name specific files or tests.

Written by the indexing model from the issue text.