Fix: Cast to timestamp prior to event time comparison

[MichelleArk]

resolves #1412
docs dbt-labs/docs.getdbt.com/#

Problem

It's not currently possible to use microbatch models with inputs that aren't of type timestamp, because BigQuery does not coerce dates or datetimes to timestamps automatically when compared to literal timestamps.

Solution

Cast event_time to timestamp on rendering, prior to comparing against timestamp literal.

https://cloud.google.com/bigquery/docs/reference/standard-sql/conversion_functions#cast_as_timestamp
works for inputs of type:

• string
• date - assumes midnight UTC
• datetime - assumes UTC
• timestamp

(shoutout to @jtcohen6 for helping with this solutioning)

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

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-bigquery contributing guide.

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-bigquery contributing guide.

[QMalcolm]

YAAAAAY