Add recency tag and conditionally enable recency tests

[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

We want to run recency tests asynchronously to building DBT models. This PR:

• Adds recency tag to all recency tests
• Conditionally enable recency tests when target is ci (to find test coverage accurately) or when the env variable IS_RECENCY_AIRFLOW_TASK is set to true. This env var is set to true only in dbt_recency_test dag. See Add separate dag for recency tests stellar-etl-airflow#500

Why

The recency tests cause alert fatigue since they run with every model build. We do not need to run them so frequently.
Also, recency tests creates issue in backfilling old tasks if newest task is failing.

Known limitations

None