Add keyspace storage settings to keyspace settings commands

[inelpandzic]

Adds the keyspace storage object from planetscale/api-bb#22099 to pscale keyspace settings and pscale keyspace update-settings.

• --disk-scaling-strategy — grow, disable, or shrink
• --max-storage — max size in bytes disks may autoscale to
• --storage — size in bytes to recreate disks at; only with shrink, must be a whole GiB

Only the flags that are passed are sent, matching the existing update-settings pattern.

# Autoscale up to 4 TiB
pscale keyspace update-settings <database> <branch> <keyspace> --org <org> \
  --disk-scaling-strategy grow --max-storage 4398046511104

# Shrink disks to 200 GiB and disable autoscaling
pscale keyspace update-settings <database> <branch> <keyspace> --org <org> \
  --disk-scaling-strategy shrink --storage 214748364800

keyspace settings output gains disk scaling strategy, storage, and max storage columns:

$ pscale keyspace settings <database> <branch> <keyspace> --org <org>
  ...   THROTTLER ENABLED   THROTTLER THRESHOLD   DISK SCALING STRATEGY   STORAGE   MAX STORAGE
  ...   Yes                 5s                    grow                    100 GiB   4.0 TiB

JSON output carries the raw API object:

"storage": {
  "storage_bytes": 107374182400,
  "max_storage_bytes": 4398046511104,
  "disk_scaling_strategy": "grow"
}

Handles https://github.com/planetscale/issues/issues/2020

[maxenglander]

What if they previously shrank a disk? In that case the API has already stored shrink scaling strategy. Seems like they ought to be able to just update the storage. Would it simplify things if we didn't do this validation in the CLI and just relied on the API.