Add intra-app pill link action to matrix.to links

[bkil]

It is useful to be able to share permalinks to people outside matrix by showing matrix.to links that I can right-click to copy the URL for them.

However, as a user of Hydrogen, I can't navigate such permalinks within the application if I don't resolve matrix.to (or have http-links disabled, etc). Please add an onclick handler that opens the respective screen and/or scrolls to the referenced message.