New schema field - secondary contact list

[cthoyt]

• update data model
• add example curation on UniProt
• add data integrity tests
• incorporate into contributors summary page
• generate new schema JSON file
• show secondary contacts below primary contact on resource page
• update contribution guide

[bgyori]

@cthoyt is this something you plan to get back to or should @nagutm look into wrapping it up? Just one clarification: what do you mean by incorporation into the "resources page"?

[cthoyt]

error seems to be due to an issue with the pandas intersphinx registry giving a cloudflare HTTP 522 error