Use configured lock plugin for locking

[soapy1]

Context

Follow up to #965 (persist the default lock plugin selection to the settings db table (and pull the default value from there))

Currently, there is only one lock plugin that can be used. In the future the selection of plugins will expand. So, users should be able to configure which plugin to use.

In order to do this, the locking plugin selection should be persisted to the settings db table. See #965 (comment) for an example of how an implementation for selecting a lock backend might look.

Depends on #1005

Value and/or benefit

Users can have a choice of which locking backend to use.

Anything else?

No response