Exclude media from sources without ContentSource record from search

[obulat]

Problem

When we add a new provider, we don't immediately add a ContentSource record to the API. This means that the media is immediately available in search results.

Description

When building an excluded source query, we should add the sources that don't have a ContentSource model to the excluded sources. To do that, we can get all sources using:

openverse/api/api/controllers/search_controller.py

Line 549 in a71cab6

sources = cache.get(key=source_cache_name)

This is where the query is built:

openverse/api/api/controllers/search_controller.py

Lines 178 to 184 in a71cab6

	if not filtered_sources:
	filtered_sources = list(
	models.ContentSource.objects.filter(filter_content=True).values_list(
	"source_identifier", flat=True
	)
	)

Alternatives

An alternative would be to add a step to the data refresh that would add new ContentSource records for all the sources that were added during the data refresh: #3548

Additional context

#2487 is related in that it added a filter for the single results: if "Hide content" for their provider is set to True, the result is not returned.

[krysal]

Reopening since the #4238 was reverted.