chore: Update discovery artifacts (#1541)

## Discovery Artifact Change Summary:
feat(analyticsadmin): update the api https://github.com/googleapis/google-api-python-client/commit/c14c42a82fbd61df00b690daa328cea212441f59
feat(appengine): update the api https://github.com/googleapis/google-api-python-client/commit/22e6b63271836d2b195191c0711d3e815d7b3f29
feat(bigquery): update the api https://github.com/googleapis/google-api-python-client/commit/5325b3654e42e393911f088e9a8358aeaf733c03
feat(content): update the api https://github.com/googleapis/google-api-python-client/commit/df08fb1f3823a5edc96e6caebe24df66e943fa36
feat(dialogflow): update the api https://github.com/googleapis/google-api-python-client/commit/eaa0b250682d593572168427d92b0c3b9438a503
feat(firestore): update the api https://github.com/googleapis/google-api-python-client/commit/89ee485ce0646fb14d4f4e1d7aae095e504cf4be
feat(gkehub): update the api https://github.com/googleapis/google-api-python-client/commit/982014c5e33c29f2e0030b950b2f2ac27afa3f8f
feat(monitoring): update the api https://github.com/googleapis/google-api-python-client/commit/440201ddeeae876ab83863def611ec39649d397c
fix(oslogin): update the api https://github.com/googleapis/google-api-python-client/commit/e940d95d04a6aba60b89ece3fd630cc0ab5cde2a
feat(retail): update the api https://github.com/googleapis/google-api-python-client/commit/58f1c1ba076ed6ecc389ddf66d0c5ac609cd9d17
feat(servicenetworking): update the api https://github.com/googleapis/google-api-python-client/commit/53d51411d39049a98df6909ae16f9c5dfee4f432
diff --git a/docs/dyn/dialogflow_v2beta1.projects.conversations.participants.html b/docs/dyn/dialogflow_v2beta1.projects.conversations.participants.html
index 1c84804..8a37552 100644
--- a/docs/dyn/dialogflow_v2beta1.projects.conversations.participants.html
+++ b/docs/dyn/dialogflow_v2beta1.projects.conversations.participants.html
@@ -1591,6 +1591,10 @@
         "payload": { # Returns a response containing a custom, platform-specific payload.
           "a_key": "", # Properties of the object.
         },
+        "telephonyTransferCall": { # Represents the signal that telles the client to transfer the phone call connected to the agent to a third-party endpoint. # A signal that the client should transfer the phone call connected to this agent to a third-party endpoint.
+          "phoneNumber": "A String", # Transfer the call to a phone number in [E.164 format](https://en.wikipedia.org/wiki/E.164).
+          "sipUri": "A String", # Transfer the call to a SIP endpoint.
+        },
         "text": { # The text response message. # Returns a text response.
           "text": [ # A collection of text responses.
             "A String",