Custom type solution for GCP helper machine types

[dacbd]

Context: #718 (comment)

Culprit:

terraform-provider-iterative/iterative/gcp/provider.go

Lines 441 to 522 in fd4a940

	instanceTypes := make(map[string]map[string]map[string]string)
	instanceTypes["m"] = map[string]map[string]string{
	"accelerator": {
	"count": "0",
	"type": "",
	},
	"machine": {
	"type": "e2-custom-8-32768",
	},
	}
	instanceTypes["l"] = map[string]map[string]string{
	"accelerator": {
	"count": "0",
	"type": "",
	},
	"machine": {
	"type": "e2-custom-32-131072",
	},
	}
	instanceTypes["xl"] = map[string]map[string]string{
	"accelerator": {
	"count": "0",
	"type": "",
	},
	"machine": {
	"type": "n2-custom-64-262144",
	},
	}
	instanceTypes["m+k80"] = map[string]map[string]string{
	"accelerator": {
	"count": "1",
	"type": "nvidia-tesla-k80",
	},
	"machine": {
	"type": "custom-8-53248",
	},
	}
	instanceTypes["l+k80"] = map[string]map[string]string{
	"accelerator": {
	"count": "4",
	"type": "nvidia-tesla-k80",
	},
	"machine": {
	"type": "custom-32-131072",
	},
	}
	instanceTypes["xl+k80"] = map[string]map[string]string{
	"accelerator": {
	"count": "8",
	"type": "nvidia-tesla-k80",
	},
	"machine": {
	"type": "custom-64-212992-ext",
	},
	}
	instanceTypes["m+v100"] = map[string]map[string]string{
	"accelerator": {
	"count": "1",
	"type": "nvidia-tesla-v100",
	},
	"machine": {
	"type": "custom-8-65536-ext",
	},
	}
	instanceTypes["l+v100"] = map[string]map[string]string{
	"accelerator": {
	"count": "4",
	"type": "nvidia-tesla-v100",
	},
	"machine": {
	"type": "custom-32-262144-ext",
	},
	}
	instanceTypes["xl+v100"] = map[string]map[string]string{
	"accelerator": {
	"count": "8",
	"type": "nvidia-tesla-v100",
	},
	"machine": {
	"type": "custom-64-524288-ext",
	},
	}

Ideally the solution is reuseable for parsing machine types for runner and task