pass additional variables for preview deployments

[sakethsomaraju]

Provide a way to pass additional variables for preview deployments.

Use case: In case, if parent deployment is configured with secrets backend, AIRFLOW__SECRETS__BACKEND_KWARGS⁠⁠⁠⁠⁠⁠⁠ will not be copied from parent deployment to preview deployment ( since it is a secret variable ). So passing it explicitly can help configuring the secret backend for preview deployment.

Workaround for this issue to create the variable in a separate step post deployment creation :

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - name: Deploy to Astro DAGS
      id: deploy_to_astro
      continue-on-error: true
      # if: ${{ github.event.inputs.deploy_type == 'DAGS' }}
      uses: astronomer/deploy-action@v0.8.0
      with:
        action: create-deployment-preview
        deployment-id: ${{ env.DEPLOYMENT_ID }}
    - name: add backend kwargs
      id: export-env
      run: |
        # install the Astro CLI
        curl -sSL https://install.astronomer.io | sudo bash -s

        # update variables
        astro deployment variable create --deployment-id ${{ steps.deploy_to_astro.outputs.preview-id	 }} AIRFLOW__SECRETS__BACKEND_KWARGS=${{ secrets.HCV_KWARGS }} --secret

The fix for this issue should enable passing variables while using action: create-deployment-preview