OCP API for optional indices

[ChristophWurst]

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Is your feature request related to a problem? Please describe.

As a Nextcloud app developer I might identify missing database indices like nextcloud/mail#9160. Applying the indices in a migration means they are always added and tables with data block the migration for x seconds/minutes/hours depending on table size.

Describe the solution you'd like

Allow apps to hook into the optional indices API of server so that they can also advertise a missing, but optional index that admins can apply later on.

Describe alternatives you've considered

N/a

Additional context

This was started in #25471 but closed due to inactivity.

[ChristophWurst]

When adding this API we might also consider adding support for replacing indices.

I noticed that occasionally we have indices that are not ideal. A migration could drop the old index (relatively cheap) and add the new one through this API (relatively expensive) but that means the instance is slow in the time between the two events. If the API took care of dropping, the time of slowness would be minimal.

[come-nc]

But we have that already, no?

https://nextcloud-server.netlify.app/classes/ocp-db-events-addmissingindicesevent

[come-nc]

Also documented in https://docs.nextcloud.com/server/latest/developer_manual/basics/storage/migrations.html#adding-indices

[ChristophWurst]

Right! I searched closed PRs but could only find the status checks API. Awesome 🙏