Add feed name and comments link to Matrix integration

[ewintr]

• [ X] I have read this document: https://miniflux.app/opinionated.html#feature-request

Currently the Matrix integration posts the article title and link of a new entry to a Matrix room. What is not shown is the feed name and the optional external 'Comments' link. This makes it less useful to follow feeds of aggregator sites like Lobste.rs or Hackernews. It would be nice if following the feed through Matrix offered the same links/functionality as in the regular web interface. Note that Matrix also supports some minimal HTML styling of messages.

For comparison, two screenshots of the same entry:

Entry in Miniflux:

Entry in Matrix:

I can probably create a pull request for this myself, the change does not seem too complicated, but I thought I'd first create an issue to see if such a feature would be welcome.