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/vlan_yang/output.json

@@ -0,0 +1,32 @@
+[
+  {
+    "vlan_id": 40,
+    "name": "test-l2-vxlan",
+    "status": "ACTIVE",
+    "vlan_type": "standard",
+    "trunk_groups": [],
+    "stp_enabled": true,
+    "vni": 110040,
+    "vni_type": "l2vni"
+  },
+  {
+    "vlan_id": 4090,
+    "name": "mlag-peer",
+    "status": "ACTIVE",
+    "vlan_type": "mlag_peer",
+    "trunk_groups": ["mlag-peer"],
+    "stp_enabled": false,
+    "vni": null,
+    "vni_type": null
+  },
+  {
+    "vlan_id": 4091,
+    "name": "mlag-ibgp",
+    "status": "ACTIVE",
+    "vlan_type": "mlag_ibgp",
+    "trunk_groups": ["mlag-peer"],
+    "stp_enabled": false,
+    "vni": null,
+    "vni_type": null
+  }
+]