Replace dayjs with luxon in mockObservations

[jmcook1186]

Types of changes

• [ ] Enhancement (project structure, spelling, grammar, formatting)
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

A description of the changes proposed in the Pull Request

Replaces dayjs datetime library with Luxon which is what we also use in time-sync

[MariamKhalatova]

@jmcook1186 Seems the branch was not up-to-date. So I updated it. Now seems working