fix: overriding image/url through env (#39)

Signed-off-by: Nianyu Shen <[email protected]>

Author: nianyush

palette-agent-install.sh.tmpl

@@ -28,8 +28,8 @@ for dep in "${dependencies[@]}"; do
     check_dependency $dep
 done
 
-IMAGE=${IMAGE_REPO}/stylus-agent-mode-linux-${ARCH}:${VERSION}
-URL=${AGENT_URL_PREFIX}/palette-agent-linux-${ARCH}
+IMAGE=${IMAGE:-${IMAGE_REPO}/stylus-agent-mode-linux-${ARCH}:${VERSION}}
+URL=${URL:-${AGENT_URL_PREFIX}/palette-agent-linux-${ARCH}}
 
 # Download edge-agent
 curl -v -L $URL -o palette-agent