Little updates and improvements for docker compose config

• Fix: links are not supported (legacy for docker official, and not supported by podman). Replacing by common network + depends_on
• Fix: version is obsolete: => remove version as this is no longer used by docker compose
• Feat: replace static exposed port values for services by env vars + default values in docker compose file allowing overriding them via .env file
• Add: .env.template file as model of env variables to customize exposed (UDATA_HTTP|REDIS|MONGODB|_EXPOSED_PORT) port in docker compose config. just copy this file to .env
• Add: .gitignore to ignore:
  • .env: override env vars for docker-compose, can contains local and sensitive data wihtout being tracked by git
  • docker-compose.override.yml: override docker-compose config by local specific values/attributes wihtout being tracked by git
• Feat: as it is a development stack using UDATA_SETTINGS & mounting a volume to share udata.cfg and making config change without being forced to rebuild image