Revision Java SDK #420

Description
Following a refactor attempt made some time ago the Java SDK has kept duplicate code and builders that are not fully functional. This makes the code quite complicated to maintain and difficult to access for contributions and reviews.
See more details #315

What we planned to do

• Cleaning
  • Cleaning and removing duplicate code #315
• Rewriting of the Error Handler
  • Timeout Exception #316
  • Throw a specific Exception instead of Exception in handlers #389
• Rewrite HTTP client
  • Switch to a fixed HTTP client library OkHttp #419
  • Add possibility to provide a generic to http methods #392
  • Add PATCH http method and updateKey() method #334
• Enhancement
  • Agree on a Json library #253
  • Make the SearchRequest class a builder #455
  • Add few missing method #473
• Update to the last version of Meilisearch
  • Changes related to the next Meilisearch release (v0.28.0) #403
  • Changes related to the next Meilisearch release (v0.29.0) #434

PR related

• Refactorization of the SDK #425