[Feature] Reword 'TestsConfigDeprecation' message to avoid confusion around deprecation timeline (not planned)

[jtcohen6]

Is this your first time submitting a feature request?

• [X] I have read the expectations for open source contributors
• [X] I have searched the existing issues, and I could not find an existing issue for this feature
• [X] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

I propose that we reword this deprecation warning in order to:

• Explain the rationale: with the introduction of "unit tests," we are differentiating these from "data tests"
• Make it clear that we are unlikely to remove support for the old nomenclature (if ever)
• Document how users can silence it

At the risk of a very wordy deprecation warning, it could be a slight language tweak and an update to the linked documentation.

Before:

09:19:21  [WARNING]: Deprecated functionality
The `tests` config has been renamed to `data_tests`. Please see
https://docs.getdbt.com/docs/build/data-tests#new-data_tests-syntax for more
information.

After:

09:19:21  [WARNING]: dbt now supports 'unit_tests'. To disambiguate from traditional 'data_tests',
dbt will encourage you to rename your 'tests' config to 'data_tests'. Please see
https://docs.getdbt.com/docs/build/data-tests#new-data_tests-syntax for more
information, or https://docs.getdbt.com/reference/global-configs/warnings to silence this warning.

Describe alternatives you've considered

Not doing this

Who will this benefit?

Users who are confused about:

• seeing this deprecation warning
• reading our publicly stated commitment to ongoing compatibility, such that dbt Core users & dbt Cloud customers should feel comfortable upgrading to / keeping on latest version

Are you interested in contributing this feature?

yes!

Anything else?

No response