Introduce support for droplet autoscaler

[asaha2]

Droplet autoscaler is currently in closed alpha and enabled for select customer.

Nit change also includes marking the new load balancer feature flags as visible in the cli text (now that these features are available since GA).

TODO:

• [x] test compiled binary
• [x] add unit tests

[asaha2]

cc @andrewsomething when you have a chance 🙏

[asaha2]

@andrewsomething Yeah should've perhaps checked in with you on this: it just seemed counter-intuitive that we accept --id as per command help text, but if we run it with --id=<id> we seem to get a Error: (droplet-autoscale.list-members) command is missing required arguments E.g.:

asaha@C02FLDHYMD6M:doctl ./builds/doctl -t $DIGITALOCEAN_TOKEN -u https://api.s2r1.internal.digitalocean.com compute droplet-autoscale list-members -h
List all members of a Droplet autoscale pool

Usage:
  doctl compute droplet-autoscale list-members [flags]

Flags:
      --format ID   Columns for output in a comma-separated list. Possible values: ID, `Status`, `Health Status`, `Unhealthy Reason`, `CPU Util`, `Mem Util`.
  -h, --help        help for list-members
      --id string   ID of the Droplet autoscale pool (required)
      --no-header   Return raw data with no headers
asaha@C02FLDHYMD6M:doctl ./builds/doctl -t $DIGITALOCEAN_TOKEN -u https://api.s2r1.internal.digitalocean.com compute droplet-autoscale list-members --id=41fd76b0-3487-4ae6-8979-d26da4b7b122
Error: (droplet-autoscale.list-members) command is missing required arguments
asaha@C02FLDHYMD6M:doctl ./builds/doctl -t $DIGITALOCEAN_TOKEN -u https://api.s2r1.internal.digitalocean.com compute droplet-autoscale list-members 41fd76b0-3487-4ae6-8979-d26da4b7b122
ID          Status    Health Status    Unhealthy Reason    CPU Util    Mem Util
11735085    active    healthy                              0.001083    0.366714
11735086    active    healthy                              0.000704    0.382897