Add support for Security Groups

[jimeh]

We want to be able to manage security groups and security group rules through Terraform.

• [x] Add support for Security Groups to go-katapult:
  • https://github.com/krystal/go-katapult/pull/103
  • https://github.com/krystal/go-katapult/pull/111
• [x] Resources:
  • [x] Add katapult_security_group resource.
  • Has repeatable inbound_rule attribute to define one or more inbound rules.
  • Has repeatable outbound_rule attribute to define one or more outbound rules.
  • [x] Add katapult_security_group_rule resource which allow managing security group rules independently.
• [x] Data Sources:
  • [x] Add katapult_security_group data source to fetch single security group.
  • [x] Add katapult_security_groups data source to fetch list of all security groups.
  • [x] Add katapult_security_group_rule data source to fetch a single security group rule.
  • [x] Add katapult_security_group_rules data source to fetch list of all rules for a single security group.

[andrewjtait]

The security groups API has now been deployed to production, and support has been added to the go-katapult client library. So this issue should be ready to be worked on.