Add missing Endpoint types for Voice

[SMadani]

Adds vbc and app endpoints for deserialisation and some cleanup around that area. See #443 for context.

[codecov-commenter]

Codecov Report

Merging #446 (0e22082) into main (2134ce0) will increase coverage by 0.06%.
The diff coverage is 52.94%.

@@             Coverage Diff              @@
##               main     #446      +/-   ##
============================================
+ Coverage     91.78%   91.84%   +0.06%     
- Complexity     1814     1837      +23     
============================================
  Files           305      308       +3     
  Lines          4869     4907      +38     
  Branches        226      225       -1     
============================================
+ Hits           4469     4507      +38     
- Misses          309      310       +1     
+ Partials         91       90       -1     

Impacted Files	Coverage Δ
...java/com/vonage/client/voice/ncco/AppEndpoint.java	100.00% <ø> (ø)
...java/com/vonage/client/voice/ncco/VbcEndpoint.java	0.00% <0.00%> (ø)
...ava/com/vonage/client/voice/WebSocketEndpoint.java	55.55% <28.57%> (+55.55%)	⬆️
...main/java/com/vonage/client/voice/AppEndpoint.java	87.50% <87.50%> (ø)
...main/java/com/vonage/client/voice/VbcEndpoint.java	87.50% <87.50%> (ø)
src/main/java/com/vonage/client/voice/Call.java	96.77% <100.00%> (+0.05%)	⬆️
...in/java/com/vonage/client/voice/PhoneEndpoint.java	100.00% <100.00%> (+4.00%)	⬆️
...main/java/com/vonage/client/voice/SipEndpoint.java	90.00% <100.00%> (+90.00%)	⬆️