✨ tests: end-to-end suite scaffold + stream-mode scenario

Add tests/e2e/ structure with shared bash helpers and the first
scenario (stream-mode): spin up real Traefik + Crowdsec via docker
compose, mount the repo as a local plugin, add a ban via cscli, verify
the bouncer blocks the matching X-Forwarded-For, then delete the
decision and verify pass-through.

Adds .github/workflows/e2e.yml with one matrix job per scenario
(stream-mode for now), and Makefile targets `e2e` and `e2e_<scenario>`
for local runs.

Refs #328

Makefile

@@ -1,7 +1,9 @@
-.PHONY: lint test vendor clean
+.PHONY: lint test vendor clean e2e
 
 export GO111MODULE=on
 
+E2E_SCENARIOS := stream-mode
+
 default: lint test
 
 lint:
@@ -13,6 +15,11 @@ test:
 yaegi_test:
 	yaegi test -v .
 
+e2e: $(addprefix e2e_,$(E2E_SCENARIOS))
+
+e2e_%:
+	./tests/e2e/scenarios/$*/run.sh
+
 vendor:
 	go mod vendor