feat: add runtime_mappings to UpdateByQuery request

## Summary `runtime_mappings` is accepted by Elasticsearch as a top-level field on `_update_by_query` request bodies (alongside `query` and `script`), but it is missing from the specification. Because the JS client (and other generated clients) derive their types from this spec, users cannot type-safely pass `runtime_mappings` to `updateByQuery` today. This was surfaced by the Security Solution team who are using runtime fields in the query's filter context via `_update_by_query`. ## What needs to change Add `runtime_mappings` to the `UpdateByQueryRequest` type in the specification (same field type already used on `SearchRequest`). ## Current workaround Until a client patch is cut, users can work around the missing type by casting the body: ```ts client.updateByQuery({ index: 'my-index', body: { runtime_mappings: { ... }, query: { ... }, script: { ... } } as any }) ```