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/tests/vxlan_yang/input.json

@@ -0,0 +1,62 @@
+{
+  "data": {
+    "InfraVTEP": {
+      "edges": [
+        {
+          "node": {
+            "source_address": {
+              "value": "10.0.255.11"
+            },
+            "udp_port": {
+              "value": 4789
+            },
+            "learn_restrict": {
+              "value": "any"
+            },
+            "source_interface": {
+              "node": {
+                "name": {
+                  "value": "Loopback1"
+                }
+              }
+            },
+            "vlan_vni_mappings": {
+              "edges": [
+                {
+                  "node": {
+                    "description": {
+                      "value": "VLAN 40 <-> VNI 110040"
+                    },
+                    "vlan": {
+                      "node": {
+                        "vlan_id": {
+                          "value": 40
+                        },
+                        "name": {
+                          "value": "test-l2-vxlan"
+                        }
+                      }
+                    },
+                    "vni": {
+                      "node": {
+                        "vni": {
+                          "value": 110040
+                        },
+                        "vni_type": {
+                          "value": "l2vni"
+                        }
+                      }
+                    }
+                  }
+                }
+              ]
+            }
+          }
+        }
+      ]
+    },
+    "InfraVRFDeviceAssignment": {
+      "edges": []
+    }
+  }
+}