Feature Request: Support `Iteration` field type

[heathsnow]

Description

I would love to be able to set the Iteration field to @current for any draft/open PRs.

Currently get this error:

Error: The following fields are not supported: Iteration (ITERATION)

[EndBug]

Totally agree, would be nice to support that as well

[janiswehen]

@EndBug Right now it seems like I have to provide the exact Iteration value like Sprint 4. But when setting, I want to automatically set to @current which then could be Sprint 4. (@previous or @next would also be nice)
So I would like to do something like

      - name: Set project iteration field to current sprint        if: github.event.action == 'closed'
        uses: kjswartz/project-fields/@v2
        with:
          operation: set
          fields: Sprint
          github_token: ${{ secrets.GITHUB_TOKEN }}
          project_url: 'https://github.com/orgs/<ORG>/projects/<NUMBER>'
          resource_url: 'https://github.com/${{ github.repository }}/issues/${{ github.event.issue.number }}'
          values: @current

instead of

      - name: Set project iteration field to current sprint        if: github.event.action == 'closed'
        uses: kjswartz/project-fields/@v2
        with:
          operation: set
          fields: Sprint
          github_token: ${{ secrets.GITHUB_TOKEN }}
          project_url: 'https://github.com/orgs/<ORG>/projects/<NUMBER>'
          resource_url: 'https://github.com/${{ github.repository }}/issues/${{ github.event.issue.number }}'
          values: Sprint 4

Or am I missing something here?