Add setting to automatically execute add-missing-indices

How to use GitHub

• Please use the 👍 reaction to show that you are interested into the same feature.
• Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
• Subscribe to receive notifications on status change and new comments.

Is your feature request related to a problem? Please describe.
Running add-missing-indices manually after upgrade on small instances isn't necessary, it could be run during the upgrade.

Describe the solution you'd like
Add an occ setting to automatically run add-missing-indices on upgrades. Many small instances would not be disrupted by running this on upgrades, so it would be useful to be configurable.

Describe alternatives you've considered
Running cronjobs, other types of scripts.

Additional context
There was some discussion of this on the forum here and many other forum threads about people being confused in how to run the command. For these kinds of users it would be maybe nice to have a setting in the UI to declare their instance as a "small" instance, to automatically configure things like this.

Start by tracing the occ db:add-missing-indices command and the upgrade flow mentioned in the issue. Review the linked forum discussion for expected behavior and configuration concerns. Done means the upgrade process can conditionally execute the command through a configurable setting without disrupting instances where it is disabled.