fix: decouple MONGODB_PORT_NUMBER from internal container port

[BrahimAfa]

Problem

Setting MONGODB_PORT_NUMBER to a non-default value (e.g. 49335) in .env breaks MongoDB replica set initialization and causes Rocket.Chat to crash on startup.

Root cause: MONGODB_PORT_NUMBER is used for both the host port and the container port in three places:

1. Port mapping (line 128): ${MONGODB_PORT_NUMBER}:${MONGODB_PORT_NUMBER} — maps host:container to the same value
2. Healthcheck (line 120): connects to mongodb:${MONGODB_PORT_NUMBER} via the Docker network
3. Init container (line 60): registers the replica set member at mongodb:${MONGODB_PORT_NUMBER}

However, mongod is started without a --port flag (line 99), so it always listens on port 27017 inside the container. When MONGODB_PORT_NUMBER is anything other than 27017, all three references point to a port nothing is listening on.

Steps to reproduce

1. Clone the repo and set MONGODB_PORT_NUMBER=49335 (or any non-default value) in .env
2. Run docker compose -f compose.database.yml -f compose.yml up -d
3. Check mongodb-init-container logs:

   MongoServerError: No host described in new configuration with
   {version: 1, term: 0} for replica set rs0 maps to this node
   

4. Check rocketchat logs:

   MongoTopologyClosedError: Topology is closed
   MongoServerSelectionError: Server selection timed out after 30000 ms
   reason: TopologyDescription { type: 'ReplicaSetNoPrimary', ... }
   

Fix

Hardcode the internal container port to 27017 (matching mongod's default) and keep MONGODB_PORT_NUMBER only for the host-side mapping. This is consistent with how NATS_PORT_NUMBER already works in this project:

ports:
  - "${NATS_BIND_IP:-127.0.0.1}:${NATS_PORT_NUMBER:-4222}:4222"
                                   

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