PYTHON-5389: Add Tags to each buildvariant and augment test skipping/tracking policy.

[Jibola]

Summary

I've added in a new stipulation on each buildvariant to require a tag specifying a language. As well, I've added linters to abide by the naming conventions on buildvariant.names as well.

Changes in this PR

• Introduced lint_config.py which checks each buildvariant has a tag of a defined language
• Added a pre-commit hook to run lint_config.py specifically on the config.yml file.
• Updated any buildvariant name without a language to now include the language in its buildvariant name
• Updated the README.md to highlight the need for a tag field with a language value on every buildvariant.

Screenshot(s)

Below shows the code catching a missing tag on a buildvariant in the config.yaml

[Copilot]

Pull Request Overview

This PR adds tagging support to build variants and updates the test notification policy in the documentation.

• Updated README.md to document the new tags field and its effect on Slack notifications.
• Modified .evergreen/config.yml to add language tags for each build variant.

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
README.md	Updated documentation to include explanation for the new "tags" field.
.evergreen/config.yml	Added a "tags" property for each build variant to support language tagging.

Comments suppressed due to low confidence (1)

README.md:190

• There is an inconsistency in the naming of the notification channel: 'dbx-ai-ml-testing-pipline-notifications' appears to be a typo compared to 'dbx-ai-ml-testing-pipeline-notifications-{language}'. Consider standardizing the channel names.

Tests are run periodically (nightly) and any failures will propagate into both the `dbx-ai-ml-testing-pipline-notifications` and `dbx-ai-ml-testing-pipeline-notifications-{language}` channel. Repo owners of this `ai-ml-testing-pipeline` library are required to join the `dbx-ai-ml-testing-pipeline-notifications`. Pipeline specific implementers must **at least** join `dbx-ai-ml-testing-pipline-notifications-{language}` (e.g. whomever implemented `langchain-js` must at least be a member of `dbx-ai-ml-testing-pipeline-notifications-js`).

[blink1073]

LGTM!