[Bug] Update CONTRIBUTING.md to Reflect Current Functional Testing Process

[pavelerokhin]

Is this a new bug?

• I believe this is a new bug
• I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

The functional testing section in the CONTRIBUTING.md file of the dbt-adaptors repository is outdated and irrelevant to the current scope of the repository. It primarily focuses on functional testing procedures that are no longer applicable.

Expected Behavior

To update the CONTRIBUTING.md file to reflect the appropriate methods for performing functional testing with both dbt-core and dbt-adapters repositories.

Steps To Reproduce

In the CONTRIBUTING.md file go to the section Functional tests

Relevant log output

No response

Environment

- OS:Ventura 13.2.1
- Python:3.9.6
- dbt-adapter:

Additional Context

No response

[Fleid]

@colin-rogers-dbt @mikealfare there may already be a ticket somewhere about that?