feat: Add toString, equals and hashCode to public domain objects

[SMadani]

Along with addressing #134, this PR aims to add convenience when debugging API responses and using the deserialised objects in collections, by implementing the equals and hashCode methods. The toString is implemented based on the class name and serialised JSON value. A reflective approach is taken to all these methods, using a common base object for JSON payloads in the form of com.vonage.client.JsonableBaseObject, which is implemented throughout the entire classs hierarchy / object graph for all JSON responses, and even some requests.

[codecov-commenter]

Codecov Report

Merging #508 (a79373c) into main (a50c7bb) will increase coverage by 0.93%.
The diff coverage is 100.00%.

❗ Current head a79373c differs from pull request most recent head 18cdbbc. Consider uploading reports for the commit 18cdbbc to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #508      +/-   ##
============================================
+ Coverage     94.26%   95.19%   +0.93%     
+ Complexity     2892     2874      -18     
============================================
  Files           426      426              
  Lines          6919     6824      -95     
  Branches        449      392      -57     
============================================
- Hits           6522     6496      -26     
+ Misses          204      200       -4     
+ Partials        193      128      -65     

Files	Coverage Δ
src/main/java/com/vonage/client/HttpWrapper.java	100.00% <ø> (ø)
...ain/java/com/vonage/client/JsonableBaseObject.java	100.00% <100.00%> (ø)
...ava/com/vonage/client/account/BalanceResponse.java	100.00% <ø> (ø)
...c/main/java/com/vonage/client/account/Country.java	100.00% <100.00%> (ø)
...com/vonage/client/account/CreateSecretRequest.java	100.00% <ø> (ø)
...com/vonage/client/account/FullPricingResponse.java	100.00% <100.00%> (ø)
...com/vonage/client/account/ListSecretsResponse.java	75.00% <100.00%> (ø)
...c/main/java/com/vonage/client/account/Network.java	100.00% <100.00%> (ø)
...m/vonage/client/account/PrefixPricingResponse.java	100.00% <100.00%> (ø)
...ava/com/vonage/client/account/PricingResponse.java	100.00% <100.00%> (ø)
... and 171 more