add generate_surrogate_key macro

[dave-connors-3]

resolves #488

This is a:

• documentation update
• bug fix with no breaking changes
• new functionality
• a breaking change

All pull requests from community contributors should target the main branch (default).

Description & motivation

This PR is a breaking change for users of the surrogate_key macro -- dbt_utils.surrogate_key now throws a compilation error, and the generate_surrogate_key macro uses a default value for the coalesce function of _dbt_utils_surrogate_key_null_ to disambiguate from empty string values.

Parity can be achieved by adding a boolean variable to your dbt project:

# dbt_project.yml
...
vars:
  dbt_utils:
    surrogate_key_treat_nulls_as_empty_strings: True

Checklist

• This code is associated with an Issue which has been triaged and accepted for development.
• 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)
  • BigQuery
  • Postgres
  • Redshift
  • Snowflake
• I followed guidelines to ensure that my changes will work on "non-core" adapters by:
  • dispatching any new macro(s) so non-core adapters can also use them (e.g. the star() source)
  • using the limit_zero() macro in place of the literal string: limit 0
  • using dbt.type_* macros instead of explicit datatypes (e.g. dbt.type_timestamp() instead of TIMESTAMP
• I have updated the README.md (if applicable)
• I have added tests & descriptions to my models (and macros if applicable)
• I have added an entry to CHANGELOG.md

[dave-connors-3]

@joellabes -- assuming tests pass here I think we're in decent shape -- decided not to take the handling for non-list args into the new world of generate_surrogate_key -- if we're breaking everyone's project, we might as well break it for the better

[joellabes]

This is wonderful! Thank you @dave-connors-3. In the interest of getting the next beta out, I'm going to accept my suggestions and merge this, but if you want to make any changes then there will be another beta release before GA I'm sure!

[joellabes]

🤩 😍