`num_instances` and `digest` cause plan noise

[llimllib]

After I set an explicit value for max_shutdown_delay_seconds (#59), my service still shows up in every plan.

Now it shows up every time because:

• it has autoscaling set, but the plan wants to add an instances value
• it has an image label, but no digest value

It seems important to me that if a service is in terraform, and hasn't changed either in the terraform or on render.com, that it ought not to appear in the plan.

[llimllib]

There are several examples in this repo where both autoscaling and num_instances are set; that doesn't make sense to me, and it seems like they in fact ought to be exclusive?

What happens if num_instances is set to 2, autoscaling is set to be anywhere from 1 to 5, and is currently at 4? Does render drop 2 instances, or ignore num_instances?

[jlkravitz]

I'm also similarly experiencing plan noise on a variety of attributes. An excerpt from a recent plan is below (we changed none of those settings).

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # module.render.render_web_service.<REDACTED> will be updated in-place
  ~ resource "render_web_service" "<REDACTED>" {
      ~ active_custom_domains         = [
          - {
              <REDACTED>
            },
        ] -> (known after apply)
      + log_stream_override           = (known after apply)
      + max_shutdown_delay_seconds    = (known after apply)
        name                          = "<REDACTED>"
      ~ notification_override         = {
          ~ notifications_to_send         = "default" -> (known after apply)
          ~ preview_notifications_enabled = "default" -> (known after apply)
        } -> (known after apply)
      ~ pull_request_previews_enabled = false -> (known after apply)
      ~ runtime_source                = {
          ~ docker = {
              ~ auto_deploy_trigger = "off" -> (known after apply)
                # (5 unchanged attributes hidden)
            }
        }
      ~ slug                          = "<REDACTED>" -> (known after apply)
        # (10 unchanged attributes hidden)
    }