Backend convert label filter to use labelName URL param

Background

Also related to &9937 (closed)

We need to use labelName as the URL param for the issues label filters in search

Proposal

The controller needs to replace labels with labelName as the expected param. The backend will need to lookup labels by name and send the label ids down into the elasticsearch query (as it currently does).

Label lookup will need to take into account if it's a global, group, or project search so labels outside of the searched scope do not accidentally get sent to Elasticsearch