Review input validation for schema

[patrickcping]

Ideally we'll have input validation on fields that might need it because of API restrictions.

The following example is the PingOne environment ID, which will use a pre-defined validator

Example (without validation):

terraform-provider-davinci/internal/service/davinci/resource_application.go

Lines 21 to 25 in 1a2d766

	"environment_id": {
	Type: schema.TypeString,
	Required: true,
	Description: "PingOne environment id",
	},

Example (with validation)
https://github.com/pingidentity/terraform-provider-pingone/blob/a2e6d79e38d7305040f9a875fca0ee259d0e76bb/internal/service/sso/resource_group.go#L34-L40

[patrickcping]

Deferred to activity that merges DaVinci capability to the PingOne Terraform provider