add structured logging with sourcegraph/log (#2)

The stabilizer has unstructured output and this is currently treated by kubernetes as error logs, causing a load of debug output to be marked as error logs.

This migrates the stabilizer to use structured logging used throughout the Sourcegraph application.

Author: bobheadxi

go.mod

@@ -6,4 +6,5 @@ require (
 	github.com/phayes/freeport v0.0.0-20180830031419-95f893ade6f2
 	github.com/prometheus/client_golang v1.13.0
 	github.com/slimsag/freeport v0.0.0-20200820000215-330cfe47953a
+	github.com/sourcegraph/log v0.0.0-20221206163500-7d93c6ad7037
 )