Hard code dispatch namespaces for fivetran_utils?

[jtcohen6]

Picks up from #3363

The _get_utils_namespaces() macro in fivetran_utils (source) works just slightly differently from the other get-namespace macros: It includes dbt_utils, alongside itself, in the list of default packages to search in. So folks with Fivetran packages installed might see this error upon upgrading to 0.19.2 / 0.20.0:

Encountered an error:
Compilation Error
  In dispatch: No macro named 'datediff' found
      Searched for: 'fivetran_utils.snowflake__datediff', 'fivetran_utils.default__datediff'

The most straightforward fix for this is just to set this variable in their project, and everything will work as anticipated:

vars:
  fivetran_utils_dispatch_list: ['dbt_utils']

This is closer to the syntax that users will need to have going forward:

dispatch:
  - macro_namespace: fivetran_utils
    search_order: ['dbt_utils', 'fivetran_utils']

At the same time, I want to take backwards compatibility really seriously, since this is otherwise a breaking change in a patch release. So this PR would shamelessly hard code backwards compatibility for that specific behavior.

I don't much like this:dbt_utils isn't actually a dependency of fivetran_utils, so it's conceivable that this might raise an error if dbt_utils isn't installed alongside it. That's true parity with current behavior, though.

I could really go either way on this one!

[jtcohen6]

[skip cii]

🤦 Well, it was worth a shot. Bound to happen anyway given the rebase.