Change notification email for group/project level notifications via the API

Problem to solve

Users are currently unable to update the notification email that notifications will be sent to at the group, subgroup, and project level via the API. This email can be updated via the UI, but in some cases, bugs prevent this from being possible.

Proposal

Similar to how it's possible to update the notification email at the global level, we should implement the ability for users to update this via the API for group/project notifications as well.

User experience goal

The user should be able to use the API with GitLab to update the notification email for specific groups and projects.

Documentation

If this feature is implemented, the following documentation will need to be updated to reflect the new ability to obtain the current group/project level notification email and update it at those levels as well.

• Group / project level notification settings
• Update group/project level notification settings