Add button to quickly message contact on Matrix

Is your feature request related to a problem? Please describe.

I would like to quickly open a Matrix chat with a contact.

Describe the solution you'd like

For a contact that has a Matrix id set, there should be a button under the contact name with the Matrix logo, that let's me quickly message the contact via Matrix, just like there are buttons for calling and mail.

Just like the other buttons, this should use the correct URI scheme, so matrix: in this case. For a contact with the Matrix id @someone:example.com this should create the link matrix:u/someone:example.com?action=chat.

Describe alternatives you've considered

Using the centralized matrix.to service.

Additional context

See https://spec.matrix.org/latest/appendices/#matrix-uri-scheme for more details on the URI scheme.