Add deploy environment config to deploy_dbt_docs workflow

[jeancochrane]

Dan noticed that the Deployments view for this repo isn't showing any successful docs deployments to GitHub Pages, despite the fact that we can see successful runs for the deploy-dbt-docs workflow. Comparing this repo to assesspy, I noticed that we're missing an environment attribute in the deploy-dbt-docs workflow, which I suspect is the culprit.

    environment:
      name: github-pages
      url: ${{ steps.deployment.outputs.page_url }}

This PR adds an environment attribute to the deploy-dbt-docs workflow in order to get our Deployments view to show the correct status of our Pages deployments.

In order to test this change, I temporarily updated the deployment workflow to deploy from this PR in 59a994c. While the deployment failed due to environment branch protection rules, you can confirm in the Deployments view that we did in fact attempt a deployment from this commit.

[dfsnow]

Nice quick fix! Thanks for taking care of this.