Add initial AppApi basic example

[tzerber]

In #2357
we discussed how AppAPI should be supported in the Docker setup. As AppAPI is now a requirement, a reliable and reproducible configuration is necessary.

After extensive testing, the configuration proposed in this merge request is the only approach I have found to be consistently stable. It has been running without issues since Nextcloud 32.0.4.

My production environment uses nginx-proxy-manager, which differs in several aspects from the existing examples in this repository. For this contribution, I have adapted the configuration as closely as possible to match the structure and conventions of the other examples while preserving the required networking differences. If any inconsistencies or errors are identified, please let me know.

This contribution currently provides an Nginx (FPM) example only. An Apache-based configuration is not included, as it has not been tested in this context. Based on the architecture, no significant differences are expected, but validation from contributors with Apache experience would be welcome.

Cheers

CC @joshtrichards

[24mu13]

Apart the actual merge of this PR, does this mean I can get rid of the missing AppAPI deploy deamon by adding in my docker-compose.yml something like this?

  appapi:
    platform: linux/amd64
    container_name: appapi
    hostname: appapi
    privileged: true
    image: ghcr.io/nextcloud/nextcloud-appapi-harp:release
    networks:
      - proxy-tier
      - appapi
    restart: always
    depends_on:
      - app
    environment:
      # NC_HAPROXY_PASSWORD needs to be at least 12 chars long. This variable exists for backward compatibility with the DSP image
      # ToDo: verify whether this variable is still required
      - NC_HAPROXY_PASSWORD=CHANGEME1234
      # HP_SHARED_KEY needs to be at least 12 chars long. 
      - HP_SHARED_KEY=CHANGEME1234
      # NC_INSTANCE_URL must be the externally accessible URL of the Nextcloud instance
      - NC_INSTANCE_URL=https://external-nextcloud.url
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock

It's not clear to me how to set NC_HAPROXY_PASSWORD & HP_SHARED_KEY by the way, even by reading the AppAPI documentation.