Improve invite users to organization feature

[klakhov]

Motivation and context

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.

How has this been tested?

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

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)
• I have increased versions of npm packages if it is necessary
  (cvat-canvas,
  cvat-core,
  cvat-data and
  cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[bsekachev]

How can we have a user without id?

[klakhov]

When user is registered (if email verification is disabled), we get user data from response of /register, and /self request is not sent. There is no id in such data

[bsekachev]

Probably we should fix /register endpoint instead

[bsekachev]

Client part LGTM
Please, fix eslint issues:

/home/runner/work/cvat/cvat/cvat-ui/src/components/invitations-page/invitations-list.tsx
Error: 5:30 error 'useEffect' is defined but never used @typescript-eslint/no-unused-vars
Error: 13:8 error 'notification' is defined but never used @typescript-eslint/no-unused-vars

[SpecLad]

Changed reject to decline.

I can still see reject everywhere in the backend code. It should be updated too.

[klakhov]

It looks we have a couple of unstable e2e tests right now:
actions_users/registration_involved/case_28_review_pipeline_feature. js
actions_projects_models/registration_involved/base_actions_project_task_user.js

They failed in this pr a couple of times(after rerun everything is ok)
And they are failing in other PRs.

I will merge this PR as its already approved, and invistigate test problems separately.