[Feature] Support for multiple worker groups with different configurations

It would be great to be able to specify multiple sets of worker statefulsets, each with different configurations. Consider some implementation like:

# values.yaml
concourse:
  workers:  # replacing concourse.worker
    default:  # this is the existing worker group
      <<: *existing-concourse-worker-map
    gpu-enabled:
      # this map merged on top of the default before templating
      tag: gpu-enabled

workers:  # replacing worker, whose new default values look like:
  default:
    <<: *existing-worker-map
  # with new groups added below
  gpu-enabled:
    # this map merged on top of the default before templating
    enabled: true

This would replace current solutions offered such as handling multiple Helm releases -- one containing all the components while the rest have web.enabled=false and postgres.enabled=false. Logically, a single Concourse cluster should be able to be managed by a single Helm release, and I think the added complexity from this feature would not outweigh the benefits.

Start by reviewing values.yaml and the existing worker configuration and StatefulSet templates; the issue does not name specific files or tests. Define how default and additional worker groups merge their configurations, then verify that one Helm release can manage groups with distinct settings instead of requiring multiple releases.