Implement firewall template and templates data sources

[zliang-akamai]

📝 Description

This is to implement the data sources for firewall template.

✔️ How to Test

make test-int PKG_NAME="firewall"

make test-int PKG_NAME="firewalltemplates"

make test-int PKG_NAME="firewalltemplate"

provider "linode" {
}

data "linode_firewall_template" "public-template" {
  slug = "public"
}

data "linode_firewall_templates" "all-template" {
}

output "firewall_template_public" {
  value = data.linode_firewall_template.public-template.id
}

output "firewall_templates" {
  value = data.linode_firewall_templates.all-template.firewall_templates
}