Fix regression where asynchronous creation of MDC events broke manual joint MDC events

This MR fixes a regression caused by e39e9c7c that causes https://git.ligo.org/emfollow/gwcelery/-/blob/0566a6e5be2cbb3b5cc9769757224572c3d862d7/gwcelery/views.py#L355-364 to fail. These changes now return a gpstime instead of a graceid in order to avoid a GraceDB call and re-enable the manual creation of joint MDC events.

This was tested using a gstlal test event:

which corresponds to https://gracedb-test.ligo.org/events/M349701/view/ (or one of the adjacent events).

gwcelery/tasks/first2years.py

@@ -181,3 +181,11 @@ def upload_event():
         |
         _vet_event.s()
     ).apply_async()
+
+    # Return gpstime to create an external MDC event with similar time
+    coinc_xml = io.BytesIO(coinc)
+    xmldoc = utils.load_fileobj(coinc_xml, contenthandler=ContentHandler)
+    coinc_inspiral_table = lsctables.CoincInspiralTable.get_table(xmldoc)
+    for row in coinc_inspiral_table:
+        # The first value always returns the correct gpstime
+        return float(row.end)