Resolve "Invite a user to clowm via email"

.pre-commit-config.yaml

clowm/api/endpoints/login.py

clowm/api/endpoints/s3key.py

clowm/api/endpoints/users.py

clowm/api/utils.py

clowm/crud/crud_user.py

clowm/db/types.py

clowm/models/user.py

clowm/smtp/send_email.py

clowm/smtp/smtp.py

clowm/smtp/templates/html/invitation.html.tmpl

clowm/smtp/templates/html/registration.html.tmpl

clowm/smtp/templates/plain/invitation.txt.tmpl

clowm/smtp/templates/plain/registration.txt.tmpl

clowm/tests/api/test_login.py

clowm/tests/api/test_users.py

clowm/tests/crud/test_resource_version.py

clowm/tests/crud/test_user.py

...ns/versions/c0ceb4bf69e3_add_invitation_token_for_user.py