feat: Add Infrahub Jinja2 transforms for VLANs, interfaces, and VXLAN (#20)

Add three GraphQL queries, Jinja2 templates, and integration tests for
generating YANG-style JSON configuration payloads from Infrahub intent data,
suitable for gNMI Set operations on Arista EOS devices.

Queries (transforms/queries/):
- vlan_intent.gql: Fetches VLANs for a device via VTEP mappings and SVI
  interfaces, including VNI associations.
- interface_intent.gql: Fetches all interface types (loopback, ethernet, vlan,
  lag) with IP addresses and type-specific attributes.
- vxlan_intent.gql: Fetches VTEP config, VLAN-to-VNI mappings, and VRF-to-VNI
  mappings (L3VNI) via VRF device assignments.

Templates (transforms/templates/):
- vlan_yang.j2: Merges VLANs from both VTEP and SVI sources, deduplicates by
  vlan_id, and emits a sorted JSON array.
- interface_yang.j2: Emits a JSON array of interfaces sorted by name, with a
  "type" discriminator field for each interface kind.
- vxlan_yang.j2: Emits a JSON object with vtep config, vlan_vni_mappings, and
  vrf_vni_mappings sections.

Integration tests (transforms/tests/):
- One test directory per transform with input.json (sample GraphQL response for
  leaf1), output.json (expected result), and test.yml config.
- Test data reflects the lab topology: leaf1 VTEP 10.0.255.11, VLAN 40 / VNI
  110040, MLAG VLANs 4090/4091, underlay Ethernet11/12.

.infrahub.yml updated with queries and jinja2_transforms sections.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

transforms/queries/vxlan_intent.gql

@@ -0,0 +1,100 @@
+query VxlanIntent($device_name: String!) {
+  # VTEP configuration for the device
+  InfraVTEP(device__name__value: $device_name) {
+    edges {
+      node {
+        source_address {
+          value
+        }
+        udp_port {
+          value
+        }
+        learn_restrict {
+          value
+        }
+        source_interface {
+          node {
+            name {
+              value
+            }
+          }
+        }
+        # VLAN-to-VNI mappings (L2 VXLAN)
+        vlan_vni_mappings {
+          edges {
+            node {
+              description {
+                value
+              }
+              vlan {
+                node {
+                  vlan_id {
+                    value
+                  }
+                  name {
+                    value
+                  }
+                }
+              }
+              vni {
+                node {
+                  vni {
+                    value
+                  }
+                  vni_type {
+                    value
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+  # VRF-to-VNI mappings (L3 VXLAN) via VRF device assignments
+  InfraVRFDeviceAssignment(device__name__value: $device_name) {
+    edges {
+      node {
+        route_distinguisher {
+          value
+        }
+        vrf {
+          node {
+            name {
+              value
+            }
+            l3vni {
+              node {
+                vni {
+                  value
+                }
+                vni_type {
+                  value
+                }
+              }
+            }
+            import_targets {
+              edges {
+                node {
+                  target {
+                    value
+                  }
+                }
+              }
+            }
+            export_targets {
+              edges {
+                node {
+                  target {
+                    value
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}