Implement an endpoint for retrieving the data for an experiment's experiment design

[ke4]

We need a new endpoint that can retrieve experiment design data for a given experiment.
This endpoint should be able to reusable for bulk and single cell applications.

We need to implement the following resources:

• Repositories for representing the exp_design and exp_design_column tables in the back-end code
• A service that uses the above implemented repository's methods to query the DB and retrieve data from there
• A controller that uses the above mentioned service the response with experiment design data for the request for a specific experiment (parameter is the experiment's accession ID)