feat(docs): Explain configuration file location for Docker Compose

[keunes]

Description

When setting up folder configuration as per https://docs.immich.app/install/config-file it wasn't clear how the configuration file should be mounted in Docker Compose. Also it was a bit confusing as different file/folder location-related variables are used in different ways.

This PR clarifies how this variable should be used icw Docker Compose.

How Has This Been Tested?

• ✅ Test A: IMMICH_CONFIG_FILE specifies the location of the config file as needed by the server application, and on the host any location is picked via the volume declaration.
• ❌ Test B: IMMICH_CONFIG_FILE specifies the location of the config file on the host, and on the server side the location /data/configuration.yml is set via the volume declaration.

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

Not used.

[bo0tzz]

Thanks! Maybe it would be good to also add an explicit callout somewhere further up the page to state that the configuration file should be mounted into the container at all?

[keunes]

Hi @bo0tzz,
Thanks for checking. Personally I'm not convinced it's needed - I would say it's obvious that any files used by the application must be mounted and it's more a question of how/where. But if you want this to be added I'm happy to update the PR.