Replace image reference with build context in docker-compose files for gitea-runner and add Dockerfile for each service

cloud-pc/gitea-runner/Dockerfile

@@ -0,0 +1,4 @@
+FROM gitea/act_runner:latest
+
+USER root
+RUN apk add --no-cache docker-cli docker-cli-compose

cloud-pc/gitea-runner/docker-compose.yml

@@ -1,6 +1,6 @@
 services:
   gitea-runner:
-    image: gitea/act_runner:latest
+    build: .
     restart: always
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock