Reduce startup time for Java samples

[kelsk]

The Java language samples have overly long build times that can be upwards of 4 minutes.

The samples should be refactored to reduce startup time as much as possible.

[averikitsch]

• Cloud Run: The entire build averages 2.5 mins with 1 min being integration tests
• Hello World and Guestbook: Deploy to staging is the longest averages 2.5min with the build is only 30-40s, polling for endpoint can also be an issue.

The main issue is the amount of time for the K8s deployment to become stable. The build is quick and there is not currently any optimization or refactoring for the app's start up time. Up to @kelsk to close or keep open.

[ace-n]

#101 may help here

[ace-n]

Pinged @kelsk who said this is good to close.