Use layout builder for farmOS dashboard

Problem/Motivation

In #3169203: farmOS 2.x Dashboard → we added a farmOS dashboard. We briefly explored using Layout Builder at this time, but ended up going with a simpler custom Controller + hook_farm_dashboard_panes() approach, which is similar to what we had in farmOS 1.x. Then in #3188797: Dashboard layout → we adopted a stacked two-column layout for the dashboard.

I'm opening this as a follow-up to those issues, so we can explore using Layout Builder more thoroughly for the farmOS dashboard.

I'd like to understand what it would require, what considerations there are, and most importantly (as it pertains to whether or not we can do this before the first beta release) what the transition from the hook-based approach to a Layout Builder approach would take (is it a breaking change? or can we somehow support both? this will determine if we need to do this before beta, or if it can wait)

Proposed resolution

TBD

Remaining tasks

TBD

User interface changes

TBD

API changes

None.

Data model changes

None.