[DRAFT] [AHMv2] Migration guide & UX documentation

[Ank4n]

Documentation for the AHM Phase 2 migration targeted towards para/dapp teams.

Covers the UX impact of functionality moving off the Relay Chain (registrar, HRMP, coretime, etc).

[Ank4n]

https://docs.polkadot.com/parachains/launch-a-parachain/deploy-to-polkadot/

Example is from PJS. Is that still maintained?

[Ank4n]

This needs update as well: https://docs.polkadot.com/parachains/launch-a-parachain/obtain-coretime/
place_order_with_credits was never documented.