refactor: Global Jackson configuration

[SMadani]

All classes in the SDK which model JSON objects use the annotations @JsonIgnoreProperties(ignoreUnknown = true) and @JsonInclude(value = JsonInclude.Include.NON_NULL). This adds needless overhead to creating new classes and nested classes, since they may be easily forgotten. It also makes classes less readable. Since this is the default policy applied across the SDK, it makes sense to configure this at the top level to avoid this repetition. The major refactoring that has occurred since v7.7.0, with the introduction of the Jsonable interface (and later, JsonableBaseObject class) that all domain classes now implement, there is a convenient way to do this using the Jsonable#createDefaultObjectMapper() method. For the rare cases where default configuration needs to be overriden, JsonableBaseObject#createJsonObjectMapper() has been added.

This PR also removes the unused and deprecated com.vonage.client.sms.HexUtil class as it is not part of the public API.

[codecov-commenter]

Codecov Report

Merging #521 (d67fa1e) into main (5f6687d) will increase coverage by 0.03%.
The diff coverage is 96.15%.

❗ Current head d67fa1e differs from pull request most recent head 2ec1405. Consider uploading reports for the commit 2ec1405 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #521      +/-   ##
============================================
+ Coverage     95.50%   95.54%   +0.03%     
+ Complexity     3348     3339       -9     
============================================
  Files           502      501       -1     
  Lines          7972     7941      -31     
  Branches        440      433       -7     
============================================
- Hits           7614     7587      -27     
+ Misses          204      200       -4     
  Partials        154      154              

Files	Coverage Δ
src/main/java/com/vonage/client/HttpWrapper.java	100.00% <ø> (ø)
src/main/java/com/vonage/client/Jsonable.java	93.33% <100.00%> (+2.02%)	⬆️
...ain/java/com/vonage/client/JsonableBaseObject.java	100.00% <100.00%> (ø)
.../com/vonage/client/VonageApiResponseException.java	67.39% <100.00%> (ø)
...onage/client/account/AccountResponseException.java	100.00% <ø> (ø)
...ava/com/vonage/client/account/BalanceResponse.java	100.00% <ø> (ø)
...c/main/java/com/vonage/client/account/Country.java	100.00% <ø> (ø)
...com/vonage/client/account/FullPricingResponse.java	100.00% <ø> (ø)
...com/vonage/client/account/ListSecretsResponse.java	33.33% <ø> (-16.67%)	⬇️
...c/main/java/com/vonage/client/account/Network.java	100.00% <ø> (ø)
... and 280 more