Supports 4489: add ISO_8601 date format

[benwaples]

Description

Adds ISO_8601 to luxon datetime formats

Motivation and Context

This PR supports: BED-4489

Why is this change required? What problem does it solve?

This format supports the ISO 8601 date format which is yyyy-mm-dd

How Has This Been Tested?

*Please describe in detail how you tested your changes.
Manually tested that the format string works as expected.

Screenshots (optional):

Types of changes

• Chore (a change that does not modify the application functionality)

Checklist:

• I have met the contributing prerequisites
  • Assigned myself to this PR
  • Added the appropriate labels
  • Associated an issue: Issues and Pull Requests README #672
  • Read the Contributing guide: https://github.com/SpecterOps/BloodHound/wiki/Contributing
• I have ensured that related documentation is up-to-date
  • Open API docs
  • Code comments (GoDocs / JSDocs)
• I have followed proper test practices
  • Added/updated tests to cover my changes
  • All new and existing tests passed