* Enhance diagnostics docs
The diagnostics docs were all in one page(`setup/reference/metrics.mdx`)
which made things a bit hard to find, and wasn't conducive to adding
new content.
Diagnostics information is now located at `setup/diagnostics` with each
section from the original `metrics.mdx` doc now having its own dedicated
page. The section will now show up in the navbar at
"Setup" > "Monitoring Your Cluster".
The content of the profiling page is expanded to include information from
https://github.com/gravitational/teleport/blob/740d184d1cfc69ae2e96c50ee738b13884fb232b/assets/monitoring/README.md#low-level-monitoring
to illustrate what the different profile types are, the information that
they capture, and how to retrieve them.
A new Distributed Tracing page is also added to instruct users on how to setup
the `tracing_service` to collect and export spans (the last open item
for #12241).
