Add public Matrix.org server statistics page with useful numbers & charts on website

Nobody has claimed this yet.

On https://matrix.org/blog/2017/07/07/a-call-to-arms-supporting-matrix/ blogpost there are very useful statistics (vital stats) about Matrix.org server and whole [matrix] network with historical charts, containing number of users in Matrix.org server, events per day, etc. But at now they are too old. I have found https://matrixstats.org/ website with some fresh stats, but it is not official and miss most interesting items. Also useful stats provide https://voyager.t2bot.io/#/stats project.

Will be good to create official stats page on Matrix.org website for display dynamic realtime (or previous day) statistics about Matrix.org server and whole [matrix] network.

**Most useful stats can be:**

- Total number of registered users in Matrix.org
- Number of active users in Matrix.org (online, or have any activity in previous day)
- Number of rooms, mirrored in Matrix.org server, and maybe Communities too
- Total events per day, and maybe split by event type
- Total number of stored events (maybe split by event type - message, member, etc)
- Total database size, media storage size
- System stats: CPU & memory usage, load, etc

Review the referenced Matrix.org blog post, matrixstats.org, and Voyager stats project to compare available metrics and charts. Determine the official data sources and scope for a public Matrix.org statistics page; done means an agreed design and implementation plan for current server and network statistics.

Written by the indexing model from the issue text.