PDE-4685 feat(core,schema): allow to set primary for outputFields

[eliangcs]

After this PR, a developer can define which output field(s) to be the primary key of an output item. For example:

{
  triggers: {
    recipe: {
      operation: {
        outputFields: [
          { key: 'authorId', primary: true },
          { key: 'name', primary: true }
        ]
      }
    }
  }
}

will tell Zapier to dedupe polling trigger results using the unique hash of (authorId, name).

If no output fields are set as primary, the field with the key id will be as the primary key for deduplication. This is the same as the current behavior.

[kola-er]

Thanks for the thorough job.

[kola-er]

What if the loop is yet to process the id field with primary set? I don't think the outputFields is always sorted to start with the id field.

[eliangcs]

You're right. Reverted the change and added a test in 7f5ef17. Thanks!