Upgrade dbt version

[amishas157]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with the jira ticket associated with the PR.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated the docs and README with the added features, breaking changes, new instructions on how to use the repository.

Release planning

• I've decided if this PR requires a new major/minor/patch version accordingly to
  semver, and I've changed the name of the BRANCH to release/* , feature/* or patch/* .

What

This PR upgrades dbt-bigquery version. Note that new versions do not allow empty tests. Either they can be set as empty list or should be omitted altogether.
https://docs.getdbt.com/docs/dbt-versions/core-upgrade/upgrading-to-v1.5#behavior-changes

An empty tests: key in a yaml file will now raise a validation error, instead of being silently skipped. You can resolve this by removing the empty tests: key, or by setting it to an empty list explicitly:

Why

To stay updated with latest dbt versions. Also, our elementary runs have been very slow with version dbt v1.3. To improve run execution time of dbt test, the upgrade would be beneficial.

Known limitations

The upgrade from v1.3 to v1.8 have some non breaking changes. I would like to note that dbt has started supporting unit test for SQL code. If we plan to add. those in future, we will need to rename tests with data_tests and then have unit test set as unit_tests. Reference