Fix bug with label_name search filter

What does this MR do and why?

Related to #479987

This MR fixes a bug found with global search for issues using the label_name param.

The fix is to take into account what search level is being requested (this is known and sent down as an option). Labels are queried differently for each level:

• global - all labels are queried
• group - group_id is sent to LabelsFinder
• project - project_id (s) and group_id (if provided) are sent to LabelsFinder

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No filtering applied: http://gdk.test:3000/search?scope=issues&search=sed

Filtering applied: https://gdk.test:3000/search?scope=issues&search=sed&label_name%5B%5D=Afterpod

User	Before	After
admin
non-admin
anonymous

How to set up and validate locally

1. setup gdk for elasticsearch
2. make sure you have issues with labels assigned to them
3. perform a global issues search, manually add a label param to the URL

• https://gdk.test:3000/search?scope=issues&search=sed&label_name%5B%5D=Afterpod

1. ensure that the filtering applies to the result
2. also test with non-admin and anonymous users