Migrate from Sentry to self-hosted GlitchTip instance

Trying something new and lightweight and more data-controlled!

I also turned down the sample rate for the performance traces feature,
because we hardly use it right now, and Sentry is always getting mad at
us for vastly exceeding our free plan quota—and like, we're not on
Sentry anymore so I imagine we have more wiggle room with that, but I
figure let's turn down the volume anyway, until we decide we want it.

config/initializers/sentry.rb

@@ -1,5 +1,5 @@
 Sentry.init do |config|
-  config.dsn = 'https://cb4b3f56c1ec50ba0667b189617446bb@o506079.ingest.sentry.io/4506180803559424'
+  config.dsn = 'https://2d3c5b739af149a0b3beb86a4d498e1f@health.openneo.net/1'
   config.breadcrumbs_logger = [:active_support_logger, :http_logger]
-  config.traces_sample_rate = 0.2
+  config.traces_sample_rate = 0.05
 end