control_mpc: add MPC control law

[dalegaard]

This adds MPC control law to main branch.

Has been extensively tested on feature/mpc_experimental branch but would like to get to main so we can get wider testing. Would appreciate final code review.

Let me know if we need to add any extra docs.

Best regards,
Lasse

[YanceyA]

edit: PR https://github.com/DangerKlippers/danger-klipper/pull/334 Now Open

@dalegaard I am working on a doc [MPC.md] update from my own branch. It should be ready for PR this weekend. Let me know if you specifically have any areas which need to be added, changed or improved.

Rough TODO:
-Adjust docs to have "experimental section" with bed function details. Remove references to BED in main section of the doc for clarity.
-Add PTC temp-power reference table
-Add any relevent discord notes, specifically around ambient temp parameter.
-Remove ambient temp parameter from primary config section to optional parameters to mitigate people placing too much emphasis on it
-Add temp wait macro
-Clean up feed forward macro section
-Add notes that MPC controls block temp and not sensor temp to mitigate user confusion.

[rogerlz]

thanks @YanceyA. I added a bit of doc to the config reference. Let me know if you want me to correct or add anything else there

[YanceyA]

Roger, a few small comments on the config. Otherwise it all looks great.

[rogerlz]

Roger, a few small comments on the config. Otherwise it all looks great.

thanks for the suggestions