ci(gameserver): build with multiple JDK versions

[andrewazores]

Welcome to Cryostat! 👋

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Based on #13

Description of the change:

Builds the gameserver container with an array of JDK versions.

Motivation for the change:

Currently, all three images are only built and published based on JDK17. Since these are all intended for testing various combinations of components to ensure compatibility and functionality, it's important for our test scenarios to cover as many supported combinations as is feasible.

How to manually test:

1. Check out PR
2. ./gameserver/build.bash