We should add a runtime option that explicitly enables embedded boundaries.

That way, we can always build AMReX and WarpX with EBs on, ship a feature-complete binary in package managers, and let users opt in to the algorithms when needed.

If disabled at runtime (default), no additional memory or runtime costs must be incurred.

Suggested Name

Following existing options https://warpx.readthedocs.io/en/latest/usage/parameters.html#embedded-boundary-conditions

warpx.eb_enabled = 0

Update: we will, after all, derive this enable/disable from existing EB runtime options.