Decentalized approvals

[Pursottam6003]

Description

Dear reviewer

In this PR I would like to brief you about a new feature where the project member can also able to invite users to the workspace

For that, I have created some endpoints which are now working fine tested using Postman

1. /users/invite/approve_user/ : for the project owner to approve the user
2. /users​/invite​/pending_users​/ : list of pending users
3. /users/invite/reject_user/ : The project owner can reject the request and delete the user
4. /users/invite/request_user/ : members can request the project owner to approve/reject the user

More changes will be pushed when I will do the testing with frontend

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Please describe the tests / checks that you performed to verify your changes. Provide instructions so we can reproduce. Please delete options that are not relevant.

• Tested the API endpoint on Postman with the 'Try it out' feature
• Tested the Models using the Django Shell
• Any other tests you performed for checking edge cases.
• Any other tests you performed for checking exceptions.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

Checklist for Models

If you added new models / made changes to exsting models, please fill this checklist.

• The primary key of the Model is an AutoField
• I have defined the __str__ method for the Model
• If the field is optional, it has been spcified explicitly
• I have added a verbose_name for each Field.
• I have added a docstring for the Model
• The model is registered on Admin Site.
• I have pushed the migrations.

Checklist for API

If you added new api endpoints / made changes to exsting endpoints, please fill this checklist.

• The endpoint is accessible through Swagger.
• The endpoint supports permissions and authentication for different roles.
• All exceptions have been handled and appropriate status code is returned to the user.
• I have added docstrings for ViewSets / Serializers.