Self-hosted instances need a way to fully recreate search index data

Currently in the official install script, only postgres-data and seaweedfs-data volumes are being backed up while the search index data meilisearch-data is not. A while ago, I moved my fluxer instance data to a new server and did not think that the meilisearch volume was important to carry over, but it turns out there is no implemented button to trigger a full re-build of an instances search indexing... so now my instance is missing a ton of search functionality. There are buttons in the admin panel to manually re-index specific guilds, but there is no way to index DM channels and group DMs (and doing every single one for every user manually is silly anyway)

I think there really should be a complete "re-build search index" button on the admin panel for times where you are restoring an instance on a new setup and have an empty meilisearch volume - fully completing all search indexing so search across the instance can be fully functional again.