feat(oapi): add mesh and meshgateway to oapi spec (#12272)

## Motivation

We want to be able to mange these resources using Terraform and need
OpenAPI spec to be able to generate that. Read the MADR if you're
interested in more details:
https://docs.google.com/document/d/1Ewe0yRx-vvAuQn5CWRFhJbBPLzdbBQ2wsQosZXk4Go8/
.

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## Implementation information

All described in the madr -
https://docs.google.com/document/d/1Ewe0yRx-vvAuQn5CWRFhJbBPLzdbBQ2wsQosZXk4Go8/edit?tab=t.0#heading=h.9m1k72xxi21x
.

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and discarded -->

## Supporting documentation

<!-- Is there a MADR? An Issue? A related PR? -->

Closes #11507

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---------

Signed-off-by: Charly Molter <[email protected]>
Signed-off-by: slonka <[email protected]>
Co-authored-by: Charly Molter <[email protected]>

api/mesh/v1alpha1/mesh/rest.yaml

@@ -0,0 +1,115 @@
+openapi: 3.0.3
+info:
+  version: v1alpha1
+  title: Kuma API
+  description: Kuma API
+  x-ref-schema-name: "Mesh"
+
+paths:
+  /meshes/{name}:
+    get:
+      summary: Returns Mesh entity
+      tags: [ "Mesh" ]
+      parameters:
+        - in: path
+          name: name
+          schema:
+            type: string
+          required: true
+          description: name of the Mesh
+      responses:
+        '200':
+          $ref: "#/components/responses/MeshItem"
+
+    put:
+      summary: Creates or Updates Mesh entity
+      tags: [ "Mesh" ]
+      parameters:
+        - in: path
+          name: name
+          schema:
+            type: string
+          required: true
+          description: name of the Mesh
+      requestBody:
+        description: Put request
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/MeshItem'
+      responses:
+        '200':
+          description: Updated
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/MeshCreateOrUpdateSuccessResponse'
+        '201':
+          description: Created
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/MeshCreateOrUpdateSuccessResponse'
+
+    delete:
+      summary: Deletes Mesh entity
+      tags: [ "Mesh" ]
+      parameters:
+        - in: path
+          name: name
+          schema:
+            type: string
+          required: true
+          description: name of the Mesh
+      responses:
+        '200':
+          description: Successful response
+
+  /meshes:
+    get:
+      summary: Returns a list of Mesh in the mesh.
+      tags: [ "Mesh" ]
+      responses:
+        '200':
+          $ref: "#/components/responses/MeshList"
+
+components:
+  schemas:
+    MeshItem:
+      $ref: 'schema.yaml'
+    MeshCreateOrUpdateSuccessResponse:
+      type: object
+      properties:
+        warnings:
+          type: array
+          description: |
+            warnings is a list of warning messages to return to the requesting Kuma API clients.
+            Warning messages describe a problem the client making the API request should correct or be aware of.
+          items:
+            type: string
+
+  responses:
+    MeshItem:
+      description: Successful response
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/MeshItem'
+    MeshList:
+      description: List
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              items:
+                type: array
+                items:
+                  $ref: "#/components/schemas/MeshItem"
+              total:
+                type: number
+                description: The total number of entities
+              next:
+                type: string
+                description: URL to the next page