This adds a build flag to `exporter.go` in `coderd/tracing` that skips
compiling the file in slim builds. This file brings in some relatively
hefty dependencies that were growing the size of the slim binary a few
megabytes. All files that import `exporter.go` also aren't included in
slim builds, so this is safe.
We end up saving 5.4MB on the Linux slim binary.
* fix: Tidy up closes for nicer output
There was a context canceled message that would appear
because of traces, and this was using the wrong close.
I don't think it was causing any specific problems, but
it could make a replica warning appear on restart.
* Fix migration and experimental
