Chim/feature/add notification service

[anannnchim]

Describe your changes

I've add 3 functions:

1. send_notification in the NotificationService class
2. get_fcm_token and notify_user in the FCMTokenRepository class

Functionalities:

1. Given a list of fcm token, send_notification will allow other parts of the program to call for sending any message or notification.
2. Given a user id, get_fcm_token will retrieve all fcm tokens for a given user and return in a list of token string.
3. Gvien a userId or a list of fcm token, send_notification can be used to send notification to users.

Issue ticket number and link

Jira

[emilymclean]

I'm generally happy with the code quality here, just a couple comments.

I would also like to see a functional test or some unit tests to ensure the credentials are loaded correctly and messaging.send receives the correct payload in the use-case of someone providing a user id as a notification destination. I ask because this code is hard to exercise and see if it works correctly.

[emilymclean]

Also you need to use pipenv and update our dependencies, none of the pipeline will work otherwise.

[emilymclean]

This looks great!