[feature] Add a request ID and include it in logs (#1476)

This adds a lightweight form of tracing to GTS. Each incoming request is
assigned a Request ID which we then pass on and log in all our log
lines. Any function that gets called downstream from an HTTP handler
should now emit a requestID=value pair whenever it logs something.

Co-authored-by: kim <grufwub@gmail.com>

internal/config/config.go

@@ -147,6 +147,8 @@ type Configuration struct {
 	AdminAccountPassword  string `name:"password" usage:"the password to set for this account"`
 	AdminTransPath        string `name:"path" usage:"the path of the file to import from/export to"`
 	AdminMediaPruneDryRun bool   `name:"dry-run" usage:"perform a dry run and only log number of items eligible for pruning"`
+
+	RequestIDHeader string `name:"request-id-header" usage:"Header to extract the Request ID from. Eg.,'X-Request-Id'"`
 }
 
 type CacheConfiguration struct {