Matrix adapter

[appdeftdev]

Changes

1. Goal 1 is to update the angular version to 19 and upgrade outdated packages and make the demo page run again
2. Goal 2 is to extend the ability of the library to speak to matrix servers.
   To enable this, a second adapter has to be implemented next to the existing xmpp-adapter with all currently available features.
3. Additional requirements:

• the demo page will be extended to run ngx-chat with xmpp or matrix adapter
• the matrix adapter has to have similar test coverage as xmpp

Checklist

• I have read the Contributing Guidelines
• I have tested the changes in this Pull Request
• My code follows the code style of this project
• My changes generate no new warnings
• I have added documentation to describe my changes
• I have made corresponding changes to the documentation
• I have signed the Contributor License Agreement (CLA)