enc-discharge to 3

Not yet implemented in sandbox, and https://chat.fhir.org/#narrow/stream/179159-cds-hooks/topic/hook.20maturity.20--.20request.20for.20implementer.20feedback!

Author: isaacvetter

docs/hooks/encounter-discharge.md

@@ -4,7 +4,7 @@
 | ---- | ----
 | specificationVersion | 1.0
 | hookVersion | 1.0
-| hookMaturity | 1 - Submitted 
+| hookMaturity | [3 - Considered](../../specification/current/#hook-maturity-model)
 
 ## Workflow