Docs: Documentation for Octez v16.0 release

Context

This merge request updates the documentation for the release of Octez version 16.0. It includes:

• New section 16.0 in the docs changelogs
• Update of the version-16 release page
• Update of the Openapi specifications

Manually testing the MR

Read the generated documentation

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR