Setup $(local_domains) from table instead of maddy.conf

# Use case

I'd like to load $(local_domains) from a table like sqlite. Right now I need to specify domains in maddy.conf but my accounts and aliases are all setup inside sqlite.

# Your idea for a solution

- [ ] I'm willing to help with the implementation

Start by reviewing how $(local_domains) is configured in maddy.conf and how account and alias data is stored in sqlite. Determine the project entry points and tests involved before choosing an implementation approach; done means local domains can be loaded from a table rather than being required in maddy.conf.

Written by the indexing model from the issue text.