Resolve: "Change slotSelectionOpensAt to automatically update date"

What does this mr do?

When creating or editing a lab, the slot selection opens at: field was not updating properly. This was due to the field being referenced back to another field and waiting for that to update.

Actions taken to fix bug

Rewrite how the fields were structured individually and actually make it wait for updates of itself.

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• A test was created to test the bug.
• I have updated the documentation accordingly.
• I adhere to the style guide.

Closes #313 (closed)