Store params and parsed params into deployment payload

[fabn]

Follow up of #322, the use case is the following: when creating a deployment one could use passed params to customise the deployment process (e.g. to pass terraform variables, or set some custom ENV variables in a kubernetes deployment).

Some environments needs to be update whenever their source branch is updated without need to trigger another deployment from scratch.

With this PR it's possible to inspect the previous deployment object and get creation params and update the environment reusing the same creation flags, proof of concept (not tested but it should work):

name: Update Environment

on:
  pull_request:
    types: [synchronize]

jobs:
  # This job get a deployment for the current branch, it assumes that at most a
  # deployment exists for any given branch, since it's a proof of concept
  # Also it assumes a previous create command like `.deploy | --vars.foo=bar --vars.bar=baz`
  payload:
    name: Retrieve payload
    runs-on: ubuntu-latest
    steps:
      - name: Get payload
        id: payload
        run: |
          gh api repos/${{ github.repository }}/deployments?ref=${{ github.event.pull_request.head.ref }}) \
           | jq -c 'first | .payload.parsed_params.vars' > payload.json
          echo vars=$(cat payload.json) >> "$GITHUB_OUTPUT"
    outputs:
      variables: ${{ steps.payload.outputs.vars }} # will contain {"foo":"bar","bar":"baz"}

  deploy:
    name: Terraform deploy
    needs: payload
    runs-on: ubuntu-latest
    steps:
      - name: Store params
        # Assuming that the payload is a JSON object with a key `params_parsed`
        run: |
          echo '${{ fromJSON(needs.payload.outputs.variables) }}' > params.tfvars.json
      - name: Setup Terraform
        uses: hashicorp/setup-terraform@v3
      - uses: actions/checkout@v4
      - name: Terraform init
        run: terraform init
      - name: Terraform apply
        run: terraform apply -auto-approve -var-file=params.tfvars.json

[GrantBirki]

@fabn thank you again for another great contribution! I have reviewed these changes and pushed a few commits to improve unit tests, add documentation, and make it so that we only ever have to parse the params once. I'll get these changes merged in for you today so that you can test them out. I'll plan on making a new release containing these changes next week. 🚀

[fabn]

Thank you for your prompt reaction 💪🏻