Enhance docs

[feteu]

Fixes #2032.

Changes proposed in this pull request:

• 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

These updates enhance readability and maintain consistency across the documentation.