Add isUndefined synthetics assertion operator (#1527)

Co-authored-by: ci.datadog-api-spec <[email protected]> b0d26f8

Author: api-clients-generation-pipeline[bot]

datadog_api_client.v1.model.html

@@ -21891,7 +21891,7 @@ <h1 id="datadog-api-client-v1-model--page-root">datadog_api_client.v1.model<a cl
 <dl class="field-list simple">
 <dt class="field-odd">Parameters<span class="colon">:</span></dt>
 <dd class="field-odd"><ul class="simple">
-<li><p><strong>value</strong> (<em>str</em>) – Must be one of [“contains”, “doesNotContain”, “is”, “isNot”, “lessThan”, “lessThanOrEqual”, “moreThan”, “moreThanOrEqual”, “matches”, “doesNotMatch”, “validates”, “isInMoreThan”, “isInLessThan”, “doesNotExist”].</p></li>
+<li><p><strong>value</strong> (<em>str</em>) – Must be one of [“contains”, “doesNotContain”, “is”, “isNot”, “lessThan”, “lessThanOrEqual”, “moreThan”, “moreThanOrEqual”, “matches”, “doesNotMatch”, “validates”, “isInMoreThan”, “isInLessThan”, “doesNotExist”, “isUndefined”].</p></li>
 <li><p><strong>_check_type</strong> (<em>bool</em>) – If True, values for parameters in openapi_types
 will be type checked and a TypeError will be raised if the wrong type is input.
 Defaults to True.</p></li>