Feat/680 new ct types

[chrismarget-j]

This PR introduces 4 new Connectivity Template resources:

• apstra_datacenter_connectivity_template_interface
• apstra_datacenter_connectivity_template_loopback
• apstra_datacenter_connectivity_template_svi
• apstra_datacenter_connectivity_template_system

The last element in the resource name (interface/loopback/svi/system) indicates the type of application point with which each resource is compatible.

The resources are organized this way because:

1. Each type of application point can accept only a prescribed set of top-level primitives, so the primitive schema differs depending on where the Connectivity Template is going to be used.
2. Creating arbitrary Connectivity Templates(say, one containing only Routing Policy primitives), while supported in the Web UI, is ultimately useless: It can't be directly used with any application point in a blueprint.

The primitive schema for each type looks like this:

• apstra_datacenter_connectivity_template_interface
  • Virtual Network (Single)
    • Static Route
    • BGP Peering (Generic System)
      • Routing Policy
  • Virtual Network (Multiple)
  • IP Link
    • BGP Peering (Generic System)
      • Routing Policy
    • BGP Peering (IP Endpoint)
      • Routing Policy
    • Dynamic BGP Peering
      • Routing Policy
    • Static Route
  • Routing Zone Constraint
• apstra_datacenter_connectivity_template_loopback
  • BGP Peering (IP Endpoint)
    • Routing Policy
• apstra_datacenter_connectivity_template_svi
  • BGP Peering (IP Endpoint)
    • Routing Policy
  • Dynamic BGP Peering
    • Routing Policy
• apstra_datacenter_connectivity_template_system
  • Custom Static Route