Changes logic of user group invitations to single operation

[Iloveall]

Description

Fixes #1685

Notes (out of scope, known isues, hints for reviewing code, ...) (optional)

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Test cases

• [ ] Case 1:

  1. Given I am the demo user
  2. When I go to this page
  3. Then I see list of group invitation
  4. Then I click on "Accept" button
  5. Then I see the message for accept

• [ ] Case 2:

  1. Given I am the demo user
  2. When I go to this page
  3. Then I see list of group invitation
  4. Then I click on "Reject" button
  5. Then I see the message for decline

[smadbe]

[auto-generated message] E2E test report on: https://algorea-static.s3.eu-central-1.amazonaws.com/branch/feature/group-invitation-single-operations/playwright-report/index.html

[smadbe]

[auto-generated message] E2E test report on: https://algorea-static.s3.eu-central-1.amazonaws.com/branch/feature/group-invitation-single-operations/playwright-report/index.html

[smadbe]

[auto-generated message] E2E test report on: https://algorea-static.s3.eu-central-1.amazonaws.com/branch/feature/group-invitation-single-operations/playwright-report/index.html

[smadbe]

column labels are wrong