fix: Add type specific date truncation functions to BigQuery

[villebro]

CATEGORY

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• Bug Fix
• Enhancement (new features, refinement)
• Refactor
• Add tests
• Build / Development Environment
• Documentation

SUMMARY

Superset currently only supports having a common truncation function for time grain expressions. BigQuery, on the other hand, requires type-specific truncation functions for all temporal types:

https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#time_trunc
https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#date_trunc
https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#datetime_trunc
https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#timestamp_trunc

This PR adds the option to specify a type-specific truncation function denoted {func} in the time grain expression. For example, the time grain expression {func}({col}, HOUR) with type DATE will yield DATE_TRUNC(my_col, HOUR). Similarly, DATETIME will yield DATETIME_TRUNC(my_col, HOUR). This also renames the config option TIME_GRAIN_ADDON_FUNCTIONS to TIME_GRAIN_ADDON_EXPRESSIONS, as they weren't really functions, but rather expressions.

BEFORE

AFTER

(note DATETIME_TRUNC instead of TIMESTAMP_TRUNC)

TEST PLAN

CI + Tested locally.

ADDITIONAL INFORMATION

• Has associated issue: closes Time Grain for BigQuery type: DATE & DATETIME is not available #9125
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

REVIEWERS

[willbarrett]

Overall looks good but it appears you have some pylint and mypy issues to resolve. Thanks for taking this on!

[codecov-io]

Codecov Report

Merging #9238 into master will not change coverage.
The diff coverage is n/a.

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  Hits         7080     7080           
  Misses       4755     4755           
  Partials      179      179

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[villebro]

Thanks @willbarrett ; fixed lint and added UPDATING.md comment

[willbarrett]

LGTM