Documentation Cleanup and Consistency Improvements

Description

Following recent commits improving clarity, grammar, and formatting across various documentation files, this issue serves to track any remaining documentation cleanup tasks.

Changes already made

• Improved clarity and formatting in CLI documentation
• Enhanced documentation for context variables and ASGI scope
• Refined language and clarity in the Connexion Cookbook
• Fixed grammar, punctuation, and typos in multiple .rst and .md files, including:
  • index.rst
  • lifespan.rst
  • middleware.rst
  • quickstart.rst
  • request.rst
  • response.rst
  • security.rst
  • swagger_ui.rst
  • testing.rst
  • v3.rst
  • validation.rst
  • README.md

Additional Info

n/a