[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/processing/search.go

@@ -57,7 +57,8 @@ func (p *processor) SearchGet(ctx context.Context, authed *oauth.Auth, search *a
 		return nil, gtserror.NewErrorBadRequest(err, err.Error())
 	}
 
-	l := log.WithFields(kv.Fields{{"query", query}}...)
+	l := log.WithContext(ctx).
+		WithFields(kv.Fields{{"query", query}}...)
 
 	searchResult := &apimodel.SearchResult{
 		Accounts: []apimodel.Account{},