[Spec Update] Redesign create_metric: default True and dict value to support create_metric_display_name

[callum-mcdata]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward change to existing dbt-semantic-interfaces functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Do measures always create metrics? In a world where all complicated metrics are defined as derived metrics on top of simple metrics, this might be true.

This Issue is complicated by the fact that create_metric = true has implications in parsing for core.

Additionally we have the create_metric_display_name property. If we want to retain this then we should make create_metric a dict to support it as a class. That way someone isn't adding the display value without create metric

Describe alternatives you've considered

No response

Who will this benefit?

No response

Are you interested in contributing this feature?

No response

Anything else?

No response