Adds unevaluatedItems schema feature

[spacether]

• Adds unevaluatedItems schema feature
• adds component schemas in sample
• tests them
• adds unevaluatedItems schema feature and turns it on in python generator documentation

Bugs found

• I found and submitted a swagger parser bug where it does not parse boolean values for unevaluatedItems schemas

A work-around for that bug is to use definitions like these instead of true/false:
true -> {}
false -> not: {}

    AnyTypeUnevaluatedItemsTrue:
      unevaluatedItems: {}
    AnyTypeUnevaluatedItemsFalse:
      unevaluatedItems:
        not: {}

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.