Add pre-commit autoupdate workflow

[mikealfare]

Problem

We moved all linting and formatting dependencies into .pre-commit-config.yml. While this consolidates these tools and isolates the dev environment from these dependencies, it also hides them from dependabot.

Solution

Add a reusable workflow:

• run pre-commit autoupdate
• run pre-commit run --all-files
• submit a PR if updates were found

CI will take care of the verification of whether new conflicts were found in the updated pre-commit hooks.

A working implementation: dbt-labs/dbt-adapters#296
The resulting PR: dbt-labs/dbt-adapters#297

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue

[emmyoop]

One more change regarding the slack notification.

[emmyoop]

Looks good