update docs.mygene.info data source table to use metadata API

[newgene]

Currently, mygene.info doc has a static data source table:

https://docs.mygene.info/en/latest/doc/data.html#data-sources

We should modify it to use the same auto-generated data src table from other API docs, e.g. from MyVariant.info:

https://docs.myvariant.info/en/latest/doc/data.html#data-sources

The docs are rendered using Sphinx, and the relevant code from myvariant.info below:

https://github.com/biothings/myvariant.info/blob/master/docs/_static/myvariant_doc.js#L8