fix: publishedAt on create (#4479)

[ColinBuyck]

This PR addresses #773

• Addresses the issue in full
• Addresses only certain aspects of the issue

Description

During Qa, it was discovered that the publishedAt date was showing as none for many open listings. This was because we were not covering the case where a user publishes a listing from scratch, never first saving it as a draft.

How Can This Be Tested/Reviewed?

Create a listing from scratch and publish it without saving it as a draft. In the partner's listing table, you should see today's date.

Author Checklist:

• Added QA notes to the issue with applicable URLs
• Reviewed in a desktop view
• Reviewed in a mobile view
• Reviewed considering accessibility
• Added tests covering the changes
• Made corresponding changes to the documentation
• Ran yarn generate:client and/or created a migration when required

Review Process:

• Read and understand the issue
• Ensure the author has added QA notes
• Review the code itself from a style point of view
• Pull the changes down locally and test that the acceptance criteria is met
• Either (1) explicitly ask a clarifying question, (2) request changes, or (3) approve the PR, even if there are very small remaining changes, if you don't need to re-review after the updates

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