[Enhancement] Update gcloud submit command in start.sh

[anish97IND]

1. Remove Beta in gcloud cloud submit command
2. Add SA flag in submit command
3. Pass env variable for service account

From a customer experience on floor (one of largest in India)- it was became tricky to set application default and even after setting it, application was not picking the desired SA. I was able to mitigate it with update in start.sh. This will benefit every one.