HubSpot
Custom properties, association labels, or a custom object.
Salesforce
Picklists, lookups, relation tables, or a custom object.
Pipedrive
A custom field, plus how to model more than one partner.
However you already record partners on a deal, Introw reads it - you configure it once on the Object Linking screen, with no RevOps work. Open your CRM above for the exact steps.