Add tox-based Integration Testing support for this package

### Description

dbt Labs is running integration tests for popular open source packages as part of continuous testing and release of dbt.

Add support for testing this package using tox, as described in [Standardizing integration tests for popular dbt packages](https://github.com/dbt-labs/dbt-core/discussions/10668).

### Acceptance Criteria

1. Tests reside in the `/integration_tests` directory.
2. Supported adapters are defined in `supported_adapters.env` at the project root. The variable `SUPPORTED_ADAPTERS` lists the supported adapters, separated by commas. (Note: Only adapters running in dbt Cloud are currently supported.)
3. [tox](https://tox.wiki/en/latest/config.html) is used for running tests.
4. Each adapter test is defined in the `tox.ini` file using the naming pattern `testenv:dbt_integration_`.
5. The `profiles.yml` for integration tests uses specific naming conventions for the target and environment variables. Examples can be found in [dbt-package-testing](https://github.com/dbt-labs/dbt-package-testing).

### Who will this benefit?

This change will enable:

- dbt Labs to test this package, ensuring that dbt Cloud customers can confidently receive continuous dbt updates ("Versionless")
- dbt Labs to proactively identify any incompatibilities or functional regressions before they are released in final versions of dbt Core OSS.
- Package maintainers to consistently test changes in the same manner as dbt Labs will test new releases.

### Final Note

dbt Labs will commence running tests only after the new tests have been released and are available in the latest package version on the [hub](https://hub.getdbt.com/).

Start by reading the linked dbt discussion and the dbt-package-testing examples, then inspect the repository root for tox.ini, supported_adapters.env, and profiles.yml. Add the integration_tests setup and adapter-specific tox environments following the stated naming and variable conventions; done means the supported adapters can run through tox and the acceptance criteria are met.

Written by the indexing model from the issue text.