fix(issues): Handle Snuba query errors in GroupTagsEndpoint (#123032)

The group tags endpoint aggregates over a 90 day window by default, and
on a large, long-lived groups the top-values query exceeds the
ClickHouse memory limit. The tagstore call was not wrapped in
handle_query_errors(), so QueryMemoryLimitExceeded escaped as an
unhandled 500.

This should really just be instrumented automatically but this will
unblock the current callsite so it maps to a 504 instead, matching every
other Snuba-backed endpoint in this package.