images/cilium: Move Envoy reference away from builder and runtime

Having the envoy reference next to the builder and runtime references
causes git context conflicts for PRs whenever either of them change in
main. Keep them separate to avoid unnecessary merge conflicts.

Signed-off-by: Jarno Rajahalme <jarno@isovalent.com>

images/cilium/Dockerfile

@@ -3,10 +3,12 @@
 
 ARG CILIUM_BUILDER_IMAGE=quay.io/cilium/cilium-builder:cc78cacf85872adae4236ee8808ef491e9b036fa@sha256:43e8907004daabcb93ce5bc5a8dcb622225bb84d555ec016218bcc3f5127844d
 ARG CILIUM_RUNTIME_IMAGE=quay.io/cilium/cilium-runtime:874a7957a8384b46fb750a151c393eb2503f4b98@sha256:36b0039e76287af586482b0657116266996d502ff7ba5b0ac4a359ba478833b4
-ARG CILIUM_ENVOY_IMAGE=quay.io/cilium/cilium-envoy:v1.29.4-e2f41ce0e07065f353b8ce28f36c01de3cfdd819@sha256:ec288baaac3758b2b0cfe2e146feb49204543961bd04f0195aae67f7b85d00f4
 
+#
 # cilium-envoy from github.com/cilium/proxy
 #
+ARG CILIUM_ENVOY_IMAGE=quay.io/cilium/cilium-envoy:v1.29.4-e2f41ce0e07065f353b8ce28f36c01de3cfdd819@sha256:ec288baaac3758b2b0cfe2e146feb49204543961bd04f0195aae67f7b85d00f4
+
 FROM ${CILIUM_ENVOY_IMAGE} as cilium-envoy
 
 #