Revert removal of QK_OUTPUT_AUTO, fixup docs to reflect.

[tzarc]

Description

As per title. Reintroduces QK_OUTPUT_AUTO/OU_AUTO, and also updates docs to reflect it.
Moved docs/features/bluetooth to docs/features/wireless for prep reasons.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[tzarc]

As discussed on #24365 (comment) .