Include route name in query stats log lines emitted by query-frontends

[charleskorn]

What this PR does

This PR builds on grafana/dskit#527 to add the route name to query stats log lines emitted by query-frontends.

This is useful when searching or analysing these log lines, particularly for APIs where the URL varies based on the request (eg. the label values API, where the URL is /prometheus/api/v1/label/{name}/values).

For example (notice the route_name value):

ts=2024-05-28T06:56:25.614545465Z caller=handler.go:374 level=info user=anonymous traceID=0c6048d9d2833e7a msg="query stats" component=query-frontend method=GET path=/prometheus/api/v1/query route_name=prometheus_api_v1_query user_agent=Grafana/10.1.5 status_code=200 response_time=4.493ms response_size_bytes=4139 query_wall_time_seconds=0.003131375 fetched_series_count=15 fetched_chunk_bytes=1429 fetched_chunks_count=30 fetched_index_bytes=0 sharded_queries=0 split_queries=0 estimated_series_count=0 queue_time_seconds=3.35e-05 param_query=up param_time=2024-05-28T06:56:25.577Z length=5m0s time_since_min_time=5m0.032958715s time_since_max_time=32.958715ms results_cache_hit_bytes=0 results_cache_miss_bytes=0 status=success

The values of route_name match those used in metrics and traces emitted by the query-frontend.

Which issue(s) this PR fixes or relates to

(none)

Checklist

• Tests updated.
• [n/a] Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [n/a] about-versioning.md updated with experimental features.