Troubleshooting doc and affordance for build temp directory

[jeffmccune]

Sometimes there are problems with a build, for example the {{.Name}} needs to be escaped, but it's unclear why it'd dropped looking at the output manifests in the deploy directory.

For this ticket, add a troubleshooting doc to the website and an env var feature flag to preserve the temp directory used for the build. This would give users a fighting chance to see what's going on. Would also be good to print out the helm command used so they could re-run it outside of holos.

holos: Component.BuildPlan

Component: #Helm & {
  Name: "external-dns"
  Chart: {
    name:     "external-dns"
    release:  "external-dns"
    version:  "1.15.0"
    repository: {
      name: "external-dns"
      url:  "https://kubernetes-sigs.github.io/external-dns"
    }
  }
  Values: {
    policy: "sync"
    txtPrefix: "external-dns."
    extraArgs: [
      "--metrics-address=:7979",
      "--aws-api-retries=3",
      "--aws-zone-type=",
      "--aws-batch-change-size=1000",
      "--domain-filter=$(CLUSTER_DOMAIN)",
      "--txt-owner-id=$(CLUSTER_NAME)",
      "--fqdn-template={{.Name}}.somedomain.com"
    ]
  }
}

[jeffmccune]

As a work around, holos render platform --log-level=debug prints the helm commands and holos show buildplans prints the values.yaml file, but it's tedious to manually reconstruct from this info.