[User Accounts] Address Book API

[the-real-chrizzo]

As a user
I want to be able to store my address book data in the cloud
to have the data available on different devices

Background
This story entails the storage of the data in our database and providing it to the web client.
The data encryption is not part of this story. However, this scope element can only be released together with the encryption (for reference this is implemented in issue https://github.com/orgs/safe-global/projects/19/views/1?pane=issue&itemId=76372592)

Acceptance criteria

• API is implemented
• API is agreed on with the web team
• Data is written in the database