Adds openapi 3.1.0 if/then/else json schema features + fixes exclusiveMax/Min bug

[spacether]

• Adds openapi 3.1.0 if/then/else json schema features
• Python generator documentation updated to show that those keywords are now supported
• Tests added to the 3.1.0 unit test client from the json schema test suite
• fixed a bug with 3.1.0 code generation where exclusiveMaximum + exclusiveMinimum data was not being accessed and stored correctly

Note:

• closed 3.1.0 info missing from schema with type unset and exclusiveMaximum/exclusiveMinimum set swagger-api/swagger-parser#1762 because work in this PR showed that it was invalid

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  mvn clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/python*.
  For Windows users, please run the script in Git BASH.