Provide clearer UI indication that only default branch is available via Elasticsearch

Problem to solve

When using Advanced Global Search it's not clear to users that only the default branch is indexed and searchable.

Further details

Regular search allows users to select the branch they're searching in. However, because elasticsearch only indexes the default branch it's not possible to search other branches. This isn't clear to users utilizing advanced global search.

Proposal

We should provide some additional indication via the UI that only the default branch is being searched.