Fixed #16054: fix incorrect compose service name in the APP_KEY generation command of the Docker env file

[brlin-tw]

This resolves the following error:

$ docker compose run --rm snipe-it php artisan key:generate --show
no such service: snipe-it

and is also how it is done in the documentation.

Refer-to: APP_KEY | Docker | Snipe-IT documentation https://snipe-it.readme.io/docs/docker#app_key

Note that the version in the master branch is also wrong, but the Contributing documentation says to target the develop branch so I'll leave it to you.

Fixes #16054

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[what-the-diff]

PR Summary

• Update to Command Instructions
  The instruction for regenerating the APP_KEY has been updated. The command to be used has been corrected from snipeit to app. This change will make the instructions more accurate, preventing potential confusion and errors when regenerating the key.