Change Build tools and Compiler target to support JDK 17

What is changed

• Change JDK compiler target from 1.6(Java 6) to 17(Java 17)
• Upgrade Gradle to 7.x(7.4.2) to support JDK 17
• Upgrade Scala version to 2.12.15 and SBT to 1.6.2 to support JDK 17 (compatibility reference)

Relevant issue numbers

• gitlab-org/gitlab#352549 (closed)