Use bulk actions to optimize `manage_relationship`

[zachdaniel]

Things to do first:

• make Ash.bulk_update support lists of tuples, w/ a record or identifier and input to update it with

[sevenseacat]

Will this allow update actions that use manage_relationship to be run atomically? ie. not require require_atomic? false?

[zachdaniel]

If the relationship is not a belongs to relationship, most likely yes.