Add docs about Gitea on same host and update docker-compose example (#2752)

Closes #1660

Taken out the part of it that's still up-to-date.
Everything else in this PR is outdated as we don't primarily use quay.io

---------

Co-authored-by: Anbraten <anton@ju60.de>
Co-authored-by: Patrick Schratz <patrick.schratz@gmail.com>

docker-compose.example.yml

@@ -2,12 +2,11 @@ version: '3'
 
 services:
   woodpecker-server:
-    build:
-      context: .
-      dockerfile: Dockerfile
-    image: woodpeckerci/woodpecker-server:local
+    image: woodpeckerci/woodpecker-server:latest
     ports:
       - 8000:8000
+    networks:
+      - woodpecker
     volumes:
       - /var/lib/woodpecker:/var/lib/woodpecker/
     environment:
@@ -19,13 +18,18 @@ services:
       - WOODPECKER_GITHUB_SECRET=${WOODPECKER_GITHUB_SECRET}
       - WOODPECKER_AGENT_SECRET=${WOODPECKER_AGENT_SECRET}
   woodpecker-agent:
-    build:
-      context: .
-      dockerfile: Dockerfile.agent
-    image: woodpeckerci/woodpecker-agent:local
+    depends_on:
+      woodpecker-server:
+        condition: service_healthy
+    image: woodpeckerci/woodpecker-agent:latest
+    networks:
+      - woodpecker
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock
     environment:
       - WOODPECKER_SERVER=woodpecker-server:9000
       - WOODPECKER_AGENT_SECRET=${WOODPECKER_AGENT_SECRET}
       - WOODPECKER_MAX_WORKFLOWS=2
+
+networks:
+  woodpecker:

docs/docs/30-administration/11-forges/30-gitea.md

@@ -20,6 +20,27 @@ services:
     [...]
 ```
 
+## Gitea on the same host
+
+If you have Gitea also running on the same host within a container, make sure the agent does have access to it.
+The agent tries to clone using the URL which Gitea reports through its API. For simplified connectivity, you should add the woodpecker agent to the same docker network as Gitea is in.
+Otherwise, the communication should go via the `docker0` gateway (usually 172.17.0.1).
+
+To configure the Docker network if the network's name is `gitea`, configure it like this:
+
+```diff
+# docker-compose.yml
+version: '3'
+
+services:
+  [...]
+  woodpecker-agent:
+    [...]
+    environment:
+      - [...]
++     - WOODPECKER_BACKEND_DOCKER_NETWORK=gitea
+```
+
 ## Registration
 
 Register your application with Gitea to create your client id and secret. You can find the OAuth applications settings of Gitea at `https://gitea.<host>/user/settings/`. It is very import the authorization callback URL matches your http(s) scheme and hostname exactly with `https://<host>/authorize` as the path.