Add example metadata.yml and document supported types

[elisabettai]

USER STORY:
A user of the cookiecutter came back with this question:

Is there a list of valid input data types, and the options (default, max, min etc) for each one? The one I am having trouble with is taking a list of numbers, like the 4th input in the webinar example at timestamp 19:07.

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1. create json-schema that defines metadata.yml including some examples #107
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2. Add an example metadata file with more advanced examples than files (e.g. the ascent runner is a good use-case) @elisabettai
3. Add link to json-form playground so users can test (e.g. https://rjsf-team.github.io/react-jsonschema-form/) @elisabettai

cc @OmkarAthavale

[pcrespov]

@elisabettai I need more input here. Perhaps we can meet offline and clarify some points ?