Collect SDK attribute from hub plugins

[pnadolny13]

Related to #624 it would be really nice to have an is_sdk attribute on all hub variants but the hub API doesnt currently return keywords which is how we label a plugin as SDK based. I created an sdk-variants-as-csv command in https://github.com/meltano/hub-utils to do one off analysis, it iterates all hub definitions and write out a CSV if its SDK or not. I need to find a way to get this data in Snowflake.