add user invite and acceptance workflow

[calellowitz]

This adds a simple user invite workflow (receive sms, visit magic link), and some other updates to how we save users based on the onboarding specs. It does not implement credentialing yet.

[snopoke]

Tests erroring on 'conflicting migrations'. I think merging main should resolve.

Lint failing (should probably install the pre-commit hooks pre-commit install):

flake8...................................................................Failed
- hook id: flake8
- exit code: 1

commcare_connect/opportunity/models.py:176:5: F811 redefinition of unused 'Meta' from line 145
commcare_connect/opportunity/views.py:221:120: E501 line too long (145 > 119 characters)
commcare_connect/users/helpers.py:41:16: F821 undefined name 'reverse'
commcare_connect/users/helpers.py:43:120: E501 line too long (161 > 119 characters)

[snopoke]

Is it necessary to have this extra dependency? This data comes straight from CCID with no way to edit it in CCC so it doesn't seem that useful to have the extra validation and support.

[calellowitz]

Seems reasonable to me. I can remove it.