Move project documents to new index

Add an Advanced Search migration that pauses indexing, creates the new index (with project mappings), moves the project documents over to the new index, and ensure reads and writes for project documents are now coming from the new index (This may be done over a few MRs, but they must be merged together)

Note: Number of Elasticsearch shards can be configured per index. Determine optimal settings for the number of shards for thew new index.

Add a the index to the existing index tests https://gitlab.com/gitlab-org/gitlab/-/tree/master/qa/qa/specs/features/ee/api/enablement/elasticsearch/index_tests