Autotuner: use structured logging instead of Sentry (#2011)

Move thousands of info-level Sentry events to logs. Query Loki rather
than downsampling events: `event.action = "run.ruby-script",
script.name = "autotuner"`

config/initializers/autotuner.rb

@@ -3,12 +3,14 @@
 Autotuner.enabled = true
 
 # This callback is called whenever a suggestion is provided by this gem.
-# You can output this report to your logging pipeline, stdout, a file,
-# or somewhere else!
-Autotuner.reporter = proc do |report|
+# Log to structured logging for query/analysis in Loki. This is called
+# once per autotuner heuristic.
+Autotuner.reporter = proc do |heuristic_report|
+  report = heuristic_report.to_s
+
   Rails.logger.info "GCAUTOTUNE: #{report}"
 
-  if Fizzy.saas?
-    Sentry.capture_message "Autotuner suggestion", level: :info, extra: { report: report.to_s }
-  end
+  RailsStructuredLogging.instrument_script "autotuner" do
+    Rails.logger.info report.to_s
+  end if defined? RailsStructuredLogging
 end