This tries to revamp/restructure the installation guide. It's renamed to
"Getting Started" as it now contains a few more things than just the
installation, especially the deployment considerations which we didn't
use to spell out as much ahead of time.
Installation is now a section with the guides on their own. I've removed
a bit of redundancy like the user creation. I also removed the rogue
reverse proxy section in the Docker guide and lifted that into the
reverse proxy section.
This adds an example on how to get Grafana Tempo up to receive spans as
well as Grafana itself to view them.
I've added this as a separate Tracing doc in the installation guide as
the Advanced one was starting to get rather full.
Fixes: #1791
