Exclude draft from UpdateAgentRequest (immutable post-create)

`draft` is a creation-time property and is not alterable on an existing
agent version. `UpdateAgentRequest` therefore should not expose it.

Switched the spread to `OmitProperties<CreateAgentVersionRequest, ""draft"">`
so PATCH /agents/{name} no longer accepts `draft`. Callers wanting a
draft version must use the explicit POST /agents/{name}/versions endpoint.

CreateAgentRequest and AgentVersionObject continue to carry `draft`.

Regenerated swaggers for v1 and virtual-public-preview - pure removals
of the `draft` property from UpdateAgentRequest only.

Author: akaila

specification/ai-foundry/data-plane/Foundry/openapi3/v1/microsoft-foundry-openapi3.json

@@ -38396,11 +38396,6 @@
                 "WorkflowAgents=V1Preview"
               ]
             }
-          },
-          "draft": {
-            "type": "boolean",
-            "description": "Whether this agent version is a draft (candidate) rather than a release. Defaults to false. Draft versions are recorded but excluded from default 'latest' resolution and are not auto-promoted.",
-            "default": false
           }
         }
       },

specification/ai-foundry/data-plane/Foundry/openapi3/virtual-public-preview/microsoft-foundry-openapi3.json

@@ -41052,11 +41052,6 @@
                 "WorkflowAgents=V1Preview"
               ]
             }
-          },
-          "draft": {
-            "type": "boolean",
-            "description": "Whether this agent version is a draft (candidate) rather than a release. Defaults to false. Draft versions are recorded but excluded from default 'latest' resolution and are not auto-promoted.",
-            "default": false
           }
         }
       },

specification/ai-foundry/data-plane/Foundry/src/agents/models.tsp

@@ -77,7 +77,7 @@ model CreateAgentRequest {
 }
 
 model UpdateAgentRequest {
-  ...CreateAgentVersionRequest;
+  ...OmitProperties<CreateAgentVersionRequest, "draft">;
 }
 
 union AgentObjectType {