Apply compression to JSON data for decrease C2S and S2S traffic

Seems at now Matrix messages in JSON format sent without compression. Will be good to apply compression to them, because JSON data have very good compression level: https://starbeamrainbowlabs.com/blog/article.php?article=posts/275-Compression-Comparison.html
So applying compression will decrease S2S and C2S traffic more than 2x times, especially considering that `m.message` contain message text in 2 formats (plain + html).

Start by reviewing the Matrix specification sections covering client-server and server-server traffic, since the issue does not name specific files, tests, or entry points. Determine how compression would be negotiated and applied to JSON messages, then document the protocol changes and interoperability expectations needed for the work to be complete.

Written by the indexing model from the issue text.