Create ClinVar submission examples with clinvar-this

[holtgrewe]

Is your feature request related to a problem? Please describe.
The ClinVar GitHub has a number of examples for the different types of submissions. They are useful to understand how to use the API.

Describe the solution you'd like
Write examples for the documentation that recreate them and explain the different steps in clinvar_api.

• Create the model clinvar_api.data structures with pythonic / snake case classes.
• Explain how to use the API client classes.
• Explain how to parse the response.

Describe alternatives you've considered
N/A

Additional context

• https://github.com/ncbi/clinvar/tree/master/submission_api_schema/sample_api_submissions