Index work items when project visibility level changes

What does this MR do and why?

Found while working on !170853 (merged)

This MR has a few related changes in it:

1. fixes a bug where project visibility changes are not updating the project's indexed work items for Advanced search.
2. does not index namespace_visibility_level for project level work items. This field is not used to query project level work items (the project_level_visibility field is). Additionally, this field is not updated when the namespace visibility level is changed for project level work items. Group associations are updated by a worker which calls group.work_items in batches. Since project level work items are not associated with a group (they are associated with a project namespace), they do not get updated by the worker. I think it's ok to not fill this field out

Note: The indexed work item data may be out of sync with the database. I've opened a follow up MR to reindex all work items that will be merged after this one. I want to keep them separate so I can backport this fix, we usually do not backport migrations

References

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!170853 (merged)

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Screenshots or screen recordings

N/A

How to set up and validate locally

1. Enable elasticseacch for gdk
2. Create a few work items in a public project, I used project id 7 (they must be issues/work items, not epic work items)
3. (query below) query elasticsearch directly to see the data, pay attention to the project_visibility_level field
4. Update the project visibility level to private
5. query elasticsearch directly to see the data, verify the project_visibility_level field was updated

curl --request POST \
  --url http://localhost:9200/gitlab-development-work_items/_search \
  --header 'Content-Type: application/json' \
  --data '{
	"size": 30,
	"query": {
		"term": {
			"project_id": 7
		}
	}
}'