Preserve mapped createdByAgent during WorkBench upload

[foozleface]

Fixes #7840
Contributed by @foozleface

When users explicitly map the createdByAgent field in WorkBench, the uploader overwrites it with the uploading user's agent instead of respecting the mapped value.

Implementation

• Add a check in upload_table.py that only auto-sets createdbyagent_id to the uploading user's agent when createdbyagent has not already been mapped as a to-one relationship in the upload plan
• The one-line change adds and "createdbyagent" not in to_one_ids to the existing conditional, so explicitly mapped values take precedence

Testing instructions

• Create a WorkBench dataset that includes a createdByAgent column mapped to a valid agent
• Upload the dataset and verify the records are created with the mapped agent as createdByAgent, not the uploading user's agent
• Verify that datasets without createdByAgent mapped still default to the uploading user's agent as before

[grantfitzsimmons]

Testing instructions

• Create a WorkBench dataset that includes a createdByAgent column mapped to a valid agent
• Upload the dataset and verify the records are created with the mapped agent as createdByAgent, not the uploading user's agent
• Verify that datasets without createdByAgent mapped still default to the uploading user's agent as before

Left (fix-7840), Right (v7.12.0-prerelease)

Works as expected!