chore: fix Dockerfile FROM quotes, gitlabci image quotes, add renovate config

.gitlab-ci.yml

@@ -1,4 +1,4 @@
-image: "docker:latest"
+image: docker:latest
 
 services:
   - "docker:dind"

Dockerfile

@@ -1,4 +1,4 @@
-FROM "alpine:3.23"
+FROM alpine:3.23
 LABEL maintainer="Cabillot Julien <dockerimages@cabillot.eu>"
 
 RUN apk add --no-cache iperf3 && \

renovate.json

@@ -0,0 +1,6 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "gitlabci": {
+    "enabled": true
+  }
+}