feat: redirect to password change view

[oxgr]

On Index view, redirect to a password change view if has_temporary_password field is set to True.

Sets to False on successful submit.

Also sets has_temporary_password to True for new onboarded users when sending first login email.

Partially addresses #372

Type of change:

• [ ] Bug fix (change which fixes an issue).
• [x] New feature (change which adds functionality).
• [x] Changes to models (requires making migrations).
• [ ] Documentation change.

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What's Changed:

• add password_set field to AuthUser
• add Password Change view
• redirect to Password Change if password_set == False
• set password_set for new users in first login email
• remove old "Change Password" tab in user dropdown (inaccessible without admin permissions)

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Screenshots:

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Affected URLs:

• 127.0.0.1:8000/
• 127.0.0.1:8000/change_password/

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Checklist:

• [x] My code follows the style guidelines of this project.
• [ ] I have performed a self-review of my own code.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have made corresponding changes to the documentation.
• [x] My changes generate no new warnings.
• [x] New and existing unit tests pass locally with my changes.