Previously, the APNS client would be reinitialized in every send.
This commit makes it so that the client is initialized with the rest of
Notification manager, to avoid performance and token management issues.
This commit brings a compilable, runnable relay draft, with logging
setup, basic README instructions, Mutex protection around shared
resources, implemented with code safety in mind
Notes:
- This is not fully tested
- The mutex design is not the most efficient, and could cause some contention on high traffic
- The REST API is not yet integrated
