The marker field-based search should match field labels as well

Currently the field-based search needs that the user knows the field name to match.
But it's impossible for a user to know them as they don't appear in the UI.

Instead we should match the labels, as a substring preferably because some labels have spaces and we don't support using quotes to match spaces currently.
My preference would be to do only match the label and stop matching the field name that have no UI reality, but Nazım would prefer to match both for backward compatibility. I don't have a super strong opinion so I'm fine with Nazım approach.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-798)

Trace the marker field-based search entry point and the label definitions in the repository; the issue names no files or tests. Reproduce the current field-name search, then verify substring matching for UI labels and resolve whether existing field-name matching remains for backward compatibility.

Written by the indexing model from the issue text.