Add delete to PipelineResource

[mathislucka]

Consult REPO.md to figure out the repository structure.

Then:

• add a delete method to the PipelineResource
• add unit tests for the new method (existing unit tests for pipeline resource)
• add integration tests (existing integration tests for pipeline resource)
• do NOT add corresponding tools

Here is how we delete a pipeline via API:

curl --request DELETE \
     --url https://api.cloud.deepset.ai/api/v1/workspaces/test-workspace/pipelines/test-pipeline \
     --header 'accept: application/json'

We get a 200 on success or a 404 or 422 if failed.

NoContentResponse is good for the success case.