Add SQL Server support

[chefferk]

Description & motivation

Adds support for SQL Server.

Similar to #49, additional refactoring could be done to the get_profile macro to reduce code duplication.

Checklist

• [x] I have verified that these changes work locally on the following warehouses (Note: it's okay if you do not have access to all warehouses, this helps us understand what has been covered):
  • [ ] Postgres
  • [ ] BigQuery
  • [ ] Snowflake
  • [ ] Redshift
  • [x] SQL Server
• [ ] I have written tests for new macros (either as dbt schema tests in integration_tests/models, dbt data tests in integration_tests/tests or integration tests in the CI workflow)
• [x] I have updated the README.md (if applicable)

[stumelius]

@chefferk This looks great, thanks :) I'll merge it right away!

[stumelius]

Closes #51