fix(gitignore): add overlay-test-server binary to ignored files

Prevents accidental commit of the overlay-test-server binary built
at the repo root (the Makefile outputs to bin/ which is already
ignored, but manual go build leaves it in the root).

Author: mattmattox

.gitignore

@@ -136,6 +136,7 @@ _site/
 .terraform/
 /node-doctor
 /node-doctor-controller
+/overlay-test-server
 
 # Log Bundles
 logs