Add Rules field to create Databases with Firewall Rules

[dvigueras]

According to the Create a New Database Cluster I've noticed the rules field was missing.

I've added this field to the DatabaseCreateRequest struct. And a new DatabaseCreateFirewallRule struct.

// DatabaseCreateFirewallRule is a rule describing an inbound source to a database
type DatabaseCreateFirewallRule struct {
	UUID  string `json:"uuid"`
	Type  string `json:"type"`
	Value string `json:"value"`
}

I didn't use the already existing DatabaseFirewallRule because of the following:

• The CreatedAt field is not present in the API Create Request. Only when you get the list of firewall rules for a Database.
• The ClusterUUID field in the documentation seems to be a bug. This field is ignored when creating a Database / doesn't make sense to be present. The Database Cluster ID is the same ID the database will have after being created.

Also I've added a test which creates a Database with two firewall rules.

[andrewsomething]

👍 Looks good to me!

Thanks for the contribution and all the feedback!