Extract the push-notification service from statusd into a separate command

[seanstrom]

Summary

• Currently, statusd uses the old approach to run status-go, by providing NodeConfig, instead of using modern CreateAccountAndLogin, LoginAccount, etc.
  • This has drawbacks that we have to keep some deprecated code just to keep statusd working.
• To replace it, we have the new status-backend which provides enough functionality. If REST API is not ideal for some needs, a new app can be implemented, which would utilize the modern status-go accounts API.
  • However, statusd is still used in notify.prod as push-notification servers for mobile app.

The goal

• We should try to extract the push-notification service from statusd into a separate command like cmd/push-notifications-server
  • This will allow us to remove the remaining usages of statusd and allow us to eventually remove the code completely.
• And we should migrate the notification infrastructure to using the new cmd/push-notifications-server instead of statusd.

[igor-sirotin]

FYI, here's the infra setup that uses statusd:
https://github.com/status-im/infra-push-notify/blob/baa1ea572ea0073310a57fd5fec24ff2d36d7d1d/ansible/group_vars/notify.yml#L20-L36

Which is loaded by this role:
https://github.com/status-im/infra-role-status-go/blob/56dbf6e8af56fc1a5cd46b3979b1f3e4bb3827f8/templates/config.json.j2

[igor-sirotin]

FYI, I was working on the status-go architecture, and it helped me understand how the Push Notification Server should look like. I've opened a draft PR:

• feat(cmd)_: push notification server #6520

This is not tested. Just shows the idea.