Add nexthop parameter to cloudstack_static_route resource

[bhouse-nexthop]

This change adds support for the nexthop parameter in static routes, which allows VPC-based routing without requiring a private gateway id.

Resource Changes:

• Add nexthop and vpc_id optional parameters to schema
• nexthop is mutually exclusive with gateway_id
• When using nexthop, vpc_id is required
• When using gateway_id, nexthop and vpc_id are not allowed
• Update resource creation logic to support both routing methods:
  • Private Gateway routing (gateway_id)
  • VPC direct routing (nexthop + vpc_id)
• Update Read function to maintain plan stability for both modes

Test Coverage:

• Add comprehensive test coverage for both routing methods
• Add testAccPreCheckStaticRouteNexthop helper to check CloudStack version
• Automatically skip nexthop tests on CloudStack versions < 4.22.0
• Version check uses CloudStack capabilities API
• Tests are skipped (not failed) on older versions for backward compatibility
• All acceptance tests passing (2/2)

Documentation:

• Update documentation with examples for both routing methods
• Document mutual exclusivity requirements
• Note CloudStack 4.22+ requirement for nexthop support

CI/CD:

• Add CloudStack 4.22.0.0 to acceptance test matrix
• Ensures tests run on both old and new CloudStack versions