Add Users API

[SMadani]

Implementation of Users API.

[codecov-commenter]

Codecov Report

Merging #468 (b6bbda0) into main (16fd480) will decrease coverage by 0.30%.
The diff coverage is 85.51%.

@@             Coverage Diff              @@
##               main     #468      +/-   ##
============================================
- Coverage     93.84%   93.55%   -0.30%     
- Complexity     2755     2884     +129     
============================================
  Files           425      443      +18     
  Lines          7006     7294     +288     
  Branches        389      440      +51     
============================================
+ Hits           6575     6824     +249     
+ Misses          280      279       -1     
- Partials        151      191      +40     

Files Changed	Coverage Δ
...ava/com/vonage/client/users/ListUsersResponse.java	66.66% <66.66%> (ø)
...rc/main/java/com/vonage/client/users/BaseUser.java	72.72% <72.72%> (ø)
...ain/java/com/vonage/client/users/channels/Sip.java	72.72% <72.72%> (ø)
...ava/com/vonage/client/users/channels/Channels.java	72.91% <72.91%> (ø)
...va/com/vonage/client/users/channels/Messenger.java	80.00% <80.00%> (ø)
...om/vonage/client/users/channels/NumberChannel.java	80.00% <80.00%> (ø)
...ain/java/com/vonage/client/users/channels/Vbc.java	80.00% <80.00%> (ø)
src/main/java/com/vonage/client/users/User.java	83.72% <83.72%> (ø)
...va/com/vonage/client/users/channels/Websocket.java	84.37% <84.37%> (ø)
...java/com/vonage/client/users/ListUsersRequest.java	97.50% <97.50%> (ø)
... and 11 more

... and 1 file with indirect coverage changes

[manchuck]