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<!-- Provide a general summary of your changes in the Title above -->

### Motivation and context
<!-- Why is this change required? What problem does it solve? If it
fixes an open
issue, please link to the issue here. Describe your changes in detail,
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This PR improves workflow with invitations to organizations. It allows
to view, accept, decline invitations to organizations (previously all
the invitations were auto-accepted).
It fixes problems with inviting unregistered users to organization
allowing them to register without invitation.


![image](https://github.com/opencv/cvat/assets/50956430/71bededa-be48-4e7a-80b6-febba86c2a3f)

![image](https://github.com/opencv/cvat/assets/50956430/773119a2-4d88-46c1-bad6-ed24734ce0c2)


### How has this been tested?
<!-- Please describe in detail how you tested your changes.
Include details of your testing environment, and the tests you ran to
see how your change affects other areas of the code, etc. -->
The best way to test this PR is to add those lines to
`cvat/settings/base.py`:
Enable email verification:
```
ACCOUNT_AUTHENTICATION_METHOD = 'username_email'
ACCOUNT_CONFIRM_EMAIL_ON_GET = True
ACCOUNT_EMAIL_REQUIRED = True
ACCOUNT_EMAIL_VERIFICATION = 'mandatory'
```

Setup console email backend
```
# Email backend settings for Django
EMAIL_BACKEND = 'django.core.mail.backends.console.EmailBackend'
```

And edit `ORG_INVITATION_CONFIRM` to `Yes`
```
ORG_INVITATION_CONFIRM = 'Yes'
```
### Checklist
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- [ ] I submit my changes into the `develop` branch
- [ ] I have created a changelog fragment <!-- see top comment in
CHANGELOG.md -->
- [ ] I have updated the documentation accordingly
- [ ] I have added tests to cover my changes
- [ ] I have linked related issues (see [GitHub docs](

https://help.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword))
- [ ] I have increased versions of npm packages if it is necessary

([cvat-canvas](https://github.com/opencv/cvat/tree/develop/cvat-canvas#versioning),

[cvat-core](https://github.com/opencv/cvat/tree/develop/cvat-core#versioning),

[cvat-data](https://github.com/opencv/cvat/tree/develop/cvat-data#versioning)
and

[cvat-ui](https://github.com/opencv/cvat/tree/develop/cvat-ui#versioning))

### License

- [ ] I submit _my code changes_ under the same [MIT License](
https://github.com/opencv/cvat/blob/develop/LICENSE) that covers the
project.
  Feel free to contact the maintainers if that's a concern.

---------

Co-authored-by: Boris Sekachev <boris@cvat.ai>
Co-authored-by: Boris Sekachev <boris.sekachev@yandex.ru>