Handle cancelling dbt Cloud jobs

[b-per]

Solves #20

Adding logic to cancel the job that was triggered if the action is still running when we cancel it.

It can be useful when workflow_dispatch is used, but also especially when people trigger CI jobs using this action.

With the additional config

on:
  - pull_request

concurrency:
  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
  cancel-in-progress: true
...

we can actually trigger dbt Cloud CI jobs from the action and if we push more commits to the PR, it will trigger a new CI job and cancel the previous one.