[ENHANCEMENT] Add Grafana dateTimeAsIso unit mapping

[abelyakin]

Description

Add the missing Grafana unit mapping for dateTimeAsIso in the CUE migration schema.

Checklist

• [ x ] Pull request has a descriptive title and context useful to a reviewer.
• [ x ] Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• [ x ] All commits have DCO signoffs.

UI Changes

• [ x ] Changes that impact the UI include screenshots and/or screencasts of the relevant changes.
• [ x ] Code follows the UI guidelines.
• [ x ] E2E tests are stable and unlikely to be flaky.
  See e2e docs for more details. Common issues include:
  • Is the data inconsistent? You need to mock API requests.
  • Does the time change? You need to use consistent time values or mock time utilities.
  • Does it have loading states? You need to wait for loading to complete.

[AntoineThebaud]

🙏