Document Actor Reminder Serializaiton

[JoshVanL]

Document:
- What API level is, how to use it

• Deprecation of JSON encoding of reminder state in v1.14
• The new protobuf storage format, and the performance benefits of using it
• Moving to protobuf cannot be reversed back into JSON
• Default is still JSON

Documentation guideline
- These annotations need to be added here https://docs.dapr.io/reference/arguments-annotations-overview/

• The description on how to use this feature and its importance needs to be added at the start of the topic https://docs.dapr.io/developing-applications/building-blocks/actors/actors-timers-reminders/ and reference the annotations. It is important to discuss 1) What the perf improvement is (~15%) and that once you go to protobuf you cannot move back to earlier releases

[yaron2]

Closed via #4058