Fixes #148

Description

Adding code for get task API so that the peoples present in volunteer group of their respective organisation will be able to see the tasks in their organisation. As a volunteer of the organisation, they will be able to see the tasks. Tests are also added for the same and swagger docs are also updated for it.

Type of Change: (Delete irrelevant options)

• Code
• Testing
• Documentation

Code/Quality Assurance Only (Delete irrelevant options)

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Tested locally along with the tests added for this API which include testing with following:

• unauthorized user
• a non-member of organisation
• invalid organisation
• get a single task
• getting a list of multiple tasks.

Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged
• Update Swagger documentation and the exported file at /docs folder
• Update requirements.txt

Code/Quality Assurance

• My changes generate no new warnings
• My PR currently breaks something (fix or feature that would cause existing functionality to not work as expected)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been published in downstream modules