qmk new-keyboard: separate dev board and MCU selection

[fauxpark]

Description

Instead of lumping everything into a giant list, we ask the user if their new keyboard project utilises a development board such as a Pro Micro, or has the microcontroller directly on the same PCB, then show the appropriate list. This has caused confusion for users in the past where they select eg. the bare RP2040 option when they are in fact using a particular RP2040-based devboard.

Types of Changes

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

Issues Fixed or Closed by This PR

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).

[fauxpark]

Porting docs have been updated to reflect current new-keyboard output, and tweaked some of it a little. I'll try to revisit more thoroughly later.