I, too, have a Google Compute Engine instance of a moodle. Tried the Google Cloud SQL which is supposed to be 'high availability' (and it is - powerful, I imagine) but ... had to change strategy after the first months bill arrived. Hope you really need HA and can afford it.
My test with MySQL and it was darn simple ... just upload an .sql file. Change config.php file and up and running. Didn't have any issues like you are describing .... that value in the table, BTW, should not include the .00 and from what you've described sounds like it should work, but isn't.
How large/space is your Google Compute Engine instance? Suggest installing a local PostGres on it and importing the PG dump to a DB right on the GCE instance. Change config.php file only for the DB info.
Does it work?
The only reason I suggest ... am assuming your import of PG dump into GCSQL went without error. But, if your moodle instance can't find that data, did the import really fail? Never did find any Google Tools that interacted with the GCSQL other than client. Did find that running mysqltuner from the GCE instance recommended some tweaks be made, but there is no my.cnf file to edit in GCSQL - had to be done via gcloud commands - kinda like MySQL Alter commands ... which needed to be made permanent. And never did find anything where I could look at logs of the GCSQL instance. :\
'spirit of sharing', Ken