S2I source builder image uses openjdk-11:latest but all other OCP deployment types use openjdk-11:1.15

Docs say to use :latest variant of the Java image (see docs) for S2I Source deployment. Other OCP deployments are using :1.15 variant (see code).

If we would stick to the same version (probably ideally the fixed one :1.15), we would have these benefits:

• Aligned versions of Java images used across OCP deployments -> more clarity for everyone
• No unexpected changes in the Java image (note the image contains bundled Maven inside - if it would be upgraded to 3.9 - not supported version - we would be in trouble see OPENJDK-1954 for more info)