fix(dbt): Support filtered COUNT DISTINCT in metrics

[Vitor-Avila]

When creating a COUNT (DISTINCT x) metric with a filter -- for example:

semantic_models:
  - name: datadiff_test
    ...
    measures:
      - name: distinct_count_test
        expr: id
        description: "The count of unique rows."
        agg: count_distinct
    dimensions:
      - name: quantity
        type: categorical
    ...

metrics:
  - name: test_distinct_metric
    description: "The number of unique rows."
    type: simple
    label: Number of CX Sent Secure Messages
    type_params:
      measure: distinct_count_test
    filter: |                                     
      {{  Dimension('id__quantity') }} > 10

The metric conversion would result in an incompatible syntax:

COUNT(CASE WHEN quantity > 10 THEN DISTINCT id END)

This PR updates the logic to replace the DISTINCT as needed:

COUNT(DISTINCT CASE WHEN quantity > 10 THEN id END)

[betodealmeida]

Lovely!