docs: fix and harmonize docker compose files (#8839)

# Which Problems Are Solved

1. Postgres spams FATAL: role "root" does not exist as mentioned in
https://github.com/zitadel/zitadel/discussions/7832 (even with -U)

2. The compose commands for a ZITADEL deployment with initial service
account key don't work out-of-the box with a non-root user, because
docker creates non-existing directories to bind-mount with root
ownership.


![image](https://github.com/user-attachments/assets/f2fc92d5-2ff4-47a4-bf4d-e9657aa2bb94)

```
time="2024-10-29T09:37:13Z" level=error msg="migration failed" caller="/home/runner/work/zitadel/zitadel/internal/migration/migration.go:68" error="open /machinekey/zitadel-admin-sa.json: permission denied" name=03_default_instance
time="2024-10-29T09:37:13Z" level=fatal msg="migration failed" caller="/home/runner/work/zitadel/zitadel/cmd/setup/setup.go:248" error="open /machinekey/zitadel-admin-sa.json: permission denied" name=03_default_instance
```

# How the Problems Are Solved

1. The branch bases on https://github.com/zitadel/zitadel/pull/8826. The
env vars are cleaned up and prettified across compose files.

2. A command is added to the docs that creates the directory with the
current users permission. The ZITADEL container runs with the current
users ID.

# Additional Context

- Replaces https://github.com/zitadel/zitadel/pull/8826
- Discussion https://github.com/zitadel/zitadel/discussions/7832
- Closes https://github.com/zitadel/zitadel/issues/7725

---------

Co-authored-by: m4tu4g <[email protected]>

.devcontainer/docker-compose.yml

@@ -8,25 +8,24 @@ services:
     network_mode: service:db
     command: sleep infinity
     environment:
-      - 'ZITADEL_DATABASE_POSTGRES_HOST=db'
-      - 'ZITADEL_DATABASE_POSTGRES_PORT=5432'
-      - 'ZITADEL_DATABASE_POSTGRES_DATABASE=zitadel'
-      - 'ZITADEL_DATABASE_POSTGRES_USER_USERNAME=zitadel'
-      - 'ZITADEL_DATABASE_POSTGRES_USER_PASSWORD=zitadel'
-      - 'ZITADEL_DATABASE_POSTGRES_USER_SSL_MODE=disable'
-      - 'ZITADEL_DATABASE_POSTGRES_ADMIN_USERNAME=postgres'
-      - 'ZITADEL_DATABASE_POSTGRES_ADMIN_PASSWORD=postgres'
-      - 'ZITADEL_DATABASE_POSTGRES_ADMIN_SSL_MODE=disable'
-      - 'ZITADEL_EXTERNALSECURE=false'
+      ZITADEL_DATABASE_POSTGRES_HOST: db
+      ZITADEL_DATABASE_POSTGRES_PORT: 5432
+      ZITADEL_DATABASE_POSTGRES_DATABASE: zitadel
+      ZITADEL_DATABASE_POSTGRES_USER_USERNAME: zitadel
+      ZITADEL_DATABASE_POSTGRES_USER_PASSWORD: zitadel
+      ZITADEL_DATABASE_POSTGRES_USER_SSL_MODE: disable
+      ZITADEL_DATABASE_POSTGRES_ADMIN_USERNAME: postgres
+      ZITADEL_DATABASE_POSTGRES_ADMIN_PASSWORD: postgres
+      ZITADEL_DATABASE_POSTGRES_ADMIN_SSL_MODE: disable
+      ZITADEL_EXTERNALSECURE: false
   db:
     image: postgres:latest
     restart: unless-stopped
     volumes:
       - postgres-data:/var/lib/postgresql/data
     environment:
+      PGUSER: postgres
       POSTGRES_PASSWORD: postgres
-      POSTGRES_USER: postgres
-      POSTGRES_DB: postgres
 
 volumes:
   postgres-data: