feat: [AXM-334] Allow easily adding Firebase credentials in Tutor

[KyryloKireiev]

Description

Allow easily adding Firebase credentials in tutor

So, to setup FIREBASE_CREDENTIALS we have to do two things:

1. Mount firebase_credentials.json to lms and cms containers;
2. Setup path to firebase_credentials.json in Tutor Plugin.

Detail instruction, how we can setup FIREBASE_CREDENTIALS:

1. Create file with FIREBASE_CREDENTIALS. For example firebase_credentials.json
2. Mount created file to LMS and CMS container:
   tutor mounts add lms:<path_to_file>/firebase_credentials.json:/openedx/<path_to_file_in_lms_container>/firebase_credentials.json
tutor mounts add cms:<path_to_file>/firebase_credentials.json:/openedx/<path_to_file_in_lms_container>/firebase_credentials.json
tutor config save - docker-compose.yml file will be regenerated. And firebase_credentials.json file will be added to lms volume.
   tutor dev restart lms cms
3. Now firebase_credentials.json is inside lms and cms containers. We can use path to this file for setup FIREBASE_CREDENTIALS_PATH constant.
   We can setup FIREBASE_CREDENTIALS_PATH in tutor plugin. There is tutor plugin example:

from tutor import hooks

hooks.Filters.ENV_PATCHES.add_item(
    (
        "lms-env",

"""
FCM_APP_NAME: "fcm-edx-platform"
ACE_ENABLED_CHANNELS: 
  - "django_email"
  - "push_notification"
FIREBASE_CREDENTIALS_PATH: "/openedx/<path_to_file_in_lms_container>/firebase_credentials.json"
"""
    )
)

hooks.Filters.ENV_PATCHES.add_item(
    (
        "cms-env",

"""
FCM_APP_NAME: "fcm-edx-platform"
ACE_ENABLED_CHANNELS: 
  - "django_email"
  - "push_notification"
FIREBASE_CREDENTIALS_PATH: "/openedx/edx-platform/firebase_credentials.json"
FIREBASE_CREDENTIALS: ""
"""
    )
)

YouTrack

https://youtrack.raccoongang.com/issue/AXM-334