[Feature] Custom calendar support

[courtneyholcomb]

Is this your first time submitting a feature request?

• [X] I have read the expectations for open source contributors
• [X] I have searched the existing issues, and I could not find an existing issue for this feature
• [X] 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

Support custom calendar spec in time spine.

time_spine:
  standard_granularity_column: date_day
  custom_granularity_columns:
      - name: fortnight
      - name: retail_month
      - name: fiscal_quarter

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