Configuration for an alternative map / location providing service.

### Your use case

#### What would you like to do?
I would like to have the possibility to display Map and location data from my own hosted Mapserver.

#### Why would you like to do it?
Im running the App and the Matrix service inside of a closed environment, like an Intranet. Therefore it is not possible to reach out to online services.

#### How would you like to achieve it?
Via an extra input inside the setting menu, maybe a conf. file like on the desktop Client if it's more viable.

### Have you considered any alternatives?

_No response_

### Additional context

I don't know if this feature already exists, if so, I'm very sorry for creating this request.

My plan was to use my company's internal offline network to host a private messaging service including my own map server.
After I set everything up, I could connect with the device and use it. That was no problem since I can configure the location of the matrix service.
What I could not do, was set the location for a custom map service, since, as far as I know, there is no option for it.

Everything that happens when I'm switching to my offline environment is, that the map data simply will not be shown - as expected when the app does not know how to reach the service.

If anyone has experience with this topic or already archived this in a way i dont know about, I would be glad for some Information.

### Are you willing to provide a PR?

No