Clarify adding tags to digitalocean_firewall

[raisedadead]

Is your feature request related to a problem? Please describe.

https://docs.digitalocean.com/products/networking/firewalls/details/limits/

The documentation recommend using tags when the droplet count is more than 10 per FW. Currently there is no way to do this via the Terraform provider. Edit: I was wrong, tags can be added using the tags attribute.

Describe the solution you'd like

Add an attribute to the provider resource to supply the tag name or id

Additional clarification in the resource documentation should help.

Describe alternatives you've considered

None available other than the UI.

Additional context

https://docs.digitalocean.com/products/networking/firewalls/details/limits/