Add .env file for agent image version and update docker-compose.yml to use dynamic image versioning for TeamCity agents; introduce a new TeamCity agent configuration.

.env

@@ -0,0 +1 @@
+AGENT_IMAGE_VERSION="2025.07.3-linux-sudo"

docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.3'
-
 networks:
   devops:
     name: devops
@@ -37,10 +35,7 @@ services:
       - '/opt/buildagent/plugins:/opt/buildagent/plugins'
       - '/opt/buildagent/temp:/opt/buildagent/temp'
       - '/opt/buildagent/tools:/opt/buildagent/tools'
-    image: jetbrains/teamcity-agent:2025.07.1-linux-sudo
-    # image: jetbrains/teamcity-agent:2023.11.1-linux-sudo
-    # image: jetbrains/teamcity-agent:2023.05.2-linux-sudo
-    # image: jetbrains/teamcity-agent:latest
+    image: jetbrains/teamcity-agent:${AGENT_IMAGE_VERSION}
   teamcity-agent-2:
     restart: always
     container_name: teamcity-agent-2
@@ -59,7 +54,27 @@ services:
       - '/opt/buildagent/plugins2:/opt/buildagent/plugins'
       - '/opt/buildagent/temp2:/opt/buildagent/temp'
       - '/opt/buildagent/tools2:/opt/buildagent/tools'
-    image: jetbrains/teamcity-agent:2025.0.1-linux-sudo
+    image: jetbrains/teamcity-agent:${AGENT_IMAGE_VERSION}
+  
+  teamcity-agent-3:
+    restart: always
+    container_name: teamcity-agent-3
+    environment:
+      - 'SERVER_URL=teamcity-server:8111'
+      - DOCKER_IN_DOCKER=start
+    user: root
+    privileged: true
+    networks:
+      - devops
+    volumes:
+      - '/teamcity/agent3:/teamcity_agent/conf'
+      - '/var/run/docker.sock:/var/run/docker.sock'
+      - '/opt/buildagent/system3:/opt/buildagent/system'
+      - '/opt/buildagent/work3:/opt/buildagent/work'
+      - '/opt/buildagent/plugins3:/opt/buildagent/plugins'
+      - '/opt/buildagent/temp3:/opt/buildagent/temp'
+      - '/opt/buildagent/tools3:/opt/buildagent/tools'
+    image: jetbrains/teamcity-agent:${AGENT_IMAGE_VERSION}
   watchtower:
     image: containrrr/watchtower
     container_name: watchtower