Configure trusted web instance to use with "Copy room link" to get `matrix.to` permalink to point people back to our own client

### Your use case

#### What would you like to do?

Allow "copy room link" to get a URL from our web client to point people _back_ to our own client

Currently, Fedora Chat (hosted by EMS) is being [configured as a "trusted server"](https://github.com/matrix-org/matrix.to/pull/233). But it's my understanding that the links generated within that web client via "Copy room link" menu items and others will still point to the general `matrix.to` server without any reference back to our instance.

#### Why would you like to do it?

We want Fedora people to be using our instance, so:

1. Their usernames match our SSO, which is good for awarding badges, metrics, and just plain other people in the project know who is who and can reasonably trust that there is no mix-up on similar usernames
2. New users get the configuration (like automatically joining Fedora Space) we have set up for new logins to our server, which will give them the best experience.
3. It's Fedora themed! We're proud of it!

#### How would you like to achieve it?

It is my understanding that once the PR referenced above is complete, links like

https://matrix.to/#/#matrix-meta-chat:fedoraproject.org?web-instance[element.io]=chat.fedoraproject.org

will redirect back to chat.fedoraproject.org. There is a setting `permalinkPrefix` which can change the `matrix.to` to something else, but setting up our own `matrix.to` seems like a heavy-handed solution. It would be nice for there to be a `permalinkTargetInstance` which could also be configured.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_