Add testcases for GET /dsmetadata API

[shreyabiradar07]

Description

This PR adds below testcases for GET /dsmetadata API

• [x] List dsmetadata specifying a valid datasource

• [x] List dsmetadata for a datasource with parameters by specifying the following parameters:

  • /dsmetadata?datasource=&verbose=false
  • /dsmetadata?datasource=&verbose=true
  • /dsmetadata?datasource=&cluster_name=&verbose=false
  • /dsmetadata?datasource=&cluster_name=&verbose=true
  • /dsmetadata?datasource=&cluster_name=&namespace=&verbose=false
  • /dsmetadata?datasource=&cluster_name=&namespace=&verbose=true

• [x] List dsmetadata with invalid parameter values for datasource, cluster_name and namespace

  • Non-existing datasource
  • Non-existing cluster_name
  • Non-existing namespace

• [x] List dsmetadata without specifying any parameters

• [x] List dsmetadata after creating a datasource but without importing metadata

• [x] List dsmetadata with datasource and namespace but without cluster_name

• [x] List the dsmetadata after deleting imported metadata

• [ ] List the dsmetadata for a datasource that has been deleted

Fixes # 1129

Type of change

• [ ] Bug fix
• [ ] New feature
• [ ] Docs update
• [ ] Breaking change (What changes might users need to make in their application due to this PR?)
• [ ] Requires DB changes
• [X] New Tests
• [ ] Updates to existing tests

How has this been tested?

• [ ] New Test X
• [X] Functional testsuite - Tested using local monitoring testsuite
• Functional test output on Jenkins - 89 with above testcases

Test Configuration

• Kubernetes clusters tested on: minikube

Checklist :dart:

• [x] Followed coding guidelines
• [x] Comments added
• [ ] Dependent changes merged
• [x] Documentation updated
• [x] Tests added or updated

Additional information

NA