feat(gatsby): detect node mutations (enabled by flag or env var)

[pieh]

Description

This adds a mode that allows detecting where nodes are being mutated directly which just doesn't work (as it used to) when LMDB is used.

This is done by wrapping nodes with recursive Proxies when being passed to plugins/user code and logging whenever set handler is called (with some exception as gatsby internals DO mutate nodes, but later they do use actions to actually update those nodes in LMDB, so those mutations are not lost)

Unfortunately we can't just have it always enabled as there is performance impact. From my testing it was mostly impacting node creation (the onCreateNode patterns unfortunately need this up front instead of "on usage" with getNode helpers or via nodeModel methods)

Documentation

• TODO: add how-to guide about this

Added guide:

Related Issues

[sc-40551]