Add database role support

[seediang]

resolves #1206
docs dbt-labs/docs.getdbt.com/#

Problem

dbt-snowflake only supports granting to Account-level database roles. Snowflake supports granting to other objects including Database Roles and Shares. However, dbt-snowflake does not.

Solution

The solution allow dbt-snowflake to manage database roles as well as existing account level roles. The configuration is extended to include a nested object_type level but also supports the original style. The original style is mapped into the new style under a "role" key.

models:
    - name: MODEL_NAME_1
      config:
        grants:
            # New syntax option
            select:
                role: [ROLE_NAME_1, ROLE_NAME_2, ...]
                database_role: [DATABASE_ROLE_NAME_1, DATABASE_ROLE_NAME_2, ...]
            insert:
                role: [ROLE_NAME_1, ROLE_NAME_2, ...]
                database_role: [DATABASE_ROLE_NAME_1, DATABASE_ROLE_NAME_2, ...]
    - name: MODEL_NAME_2
      config:
        grants:
            # Also preserve existing syntax for full backwards compatibility
            select: [ROLE_NAME_1, ROLE_NAME_2, ...]

The solution has added a number of python functions to the adapter. Originally these were implemented as macros but the logic was also required in python for the automated tests. Rather than duplicate the logic it was moved into python and made available in the jinja context.

The new functions are below. I believe in the long term these would make sense migrating into the dbt-adapter project.

• standardize_grant_config
• diff_of_grants

The solution also introduces three new macros, which are similar to existing ones but take an additional object_type parameter ie role or database_role:

• get_grant_sql_by_type
• get_revoke_sql_by_type
• get_dcl_statement_list_by_type

Areas that need advice

1. The existing test_grants.py has been patched to make use of the new functions and the tests are passing. This is not the cleanest and any suggestion for improvement would be appreciated.
2. The best way to extended the current tests to support roles in the new style.
3. The best way to include database roles in the functional tests.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[seediang]

To allow tests that use database_roles, this fixture has been added at session level to create 3 database roles in a similar style to the account-level roles that exist in the testing framework.