internal/{queue,worker}: add worker source param

When a request is enqueued via the /enqueue endpoint, add a
source=worker query param so that it is clear from the logs where this
request came from.

Change-Id: I396bb8a952640c244e0b217e48356e8088ed5eb0
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/349530
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
diff --git a/internal/queue/queue.go b/internal/queue/queue.go
index 8c1c37b..5eb9bc2 100644
--- a/internal/queue/queue.go
+++ b/internal/queue/queue.go
@@ -167,6 +167,7 @@
 	DisableProxyFetchValue = "off"
 	SourceParam            = "source"
 	SourceFrontendValue    = "frontend"
+	SourceWorkerValue      = "worker"
 )
 
 func (q *GCP) newTaskRequest(modulePath, version string, opts *Options) *taskspb.CreateTaskRequest {
diff --git a/internal/worker/server.go b/internal/worker/server.go
index dd57f8c..6fe45f3 100644
--- a/internal/worker/server.go
+++ b/internal/worker/server.go
@@ -461,6 +461,7 @@
 		opts := queue.Options{
 			Suffix:            suffixParam,
 			DisableProxyFetch: shouldDisableProxyFetch(m),
+			Source:            queue.SourceWorkerValue,
 		}
 		sem <- struct{}{}
 		go func() {