[FEATURE] Implement Snakemake export supported by the current APE version

[eladrion]

Feature Description

Provide Snakemake export API and classes.

Problem Statement

APE main branch supports Snakemake export but RestAPE does not yet provide the API to expose this functionality.

Proposed Solution

Implement the necessary functionality analogously to the CWL export

Alternatives Considered

Use Cases

The implemented functionality is to be reused by Workflomics-frontend, for example, to enable users to download Snakemake workflows in the frontend.

Additional Context

[eladrion]

Will take that over and delegate frontend

[eladrion]

Resolved with #95