[Spec Update] Refactor metric type_params to instead be separate defined metric interfaces

[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

@QMalcolm can you offer more context here on what this issue entails?

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