Fix returning 5XX for limits errors in series API

[harry671003]

What this PR does:

• This PR fixes a bug in the /api/v1/series which returns status code 500 when the query hits the limits.
• The validation error is converted into a 422 error here: https://github.com/cortexproject/cortex/blob/master/pkg/querier/error_translate_queryable.go#L39
• Therefore the error should be wrapped inside validation.LimitError. We do this in other APIs: https://github.com/cortexproject/cortex/blob/master/pkg/distributor/query.go#L326

level=warn ts=2023-02-23T00:00:00Z caller=logging.go:86 msg="POST /prometheus/api/v1/series (500) 1.232489841s Response: \"{\\\"status\\\":\\\"error\\\",\\\"errorType\\\":\\\"internal\\\",\\\"error\\\":\\\"the query hit the aggregated data size limit (limit: 1000000000 bytes)\\\"}\" ws: false; Accept: application/json, text/plain, <TRUNCATED>

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yeya24]

Thanks for the fix!