Move sending invitation email from hook_ENTITY_TYPE_insert to service

+1 for this, it makes the module more useful.

Code review: Looks solid, after all it's just moving code around and making it pluggable.

Did not test it (and the module has not moved its tests to gitlab ci).

@mariia: You may want to learn adding MRs, it has lots of benefits (maintainers often like it, gitlab ci, and more :-).

I have updated the code with latest changes from RC branch, plus renamed the classes to keep the same naming everywhere

Automatically closed - issue fixed for 2 weeks with no activity.