[go-migration] JRE type switched when JBP_CONFIG_<JRE_TYPE> is specified without taking in concern JBP_CONFIG_COMPONENTS

[kiril-keranov]

The current behavior in the java-buildpack with respect to the type of JRE used is that by default the JBP_CONFIG_COMPONENTS value is:

JBP_CONFIG_COMPONENTS: '{jres: ["JavaBuildpack::Jre::OpenJdkJRE"]}'

if you want to use different JRE type you have to specify like:

...
env:
    JBP_CONFIG_COMPONENTS: '{jres: ["JavaBuildpack::Jre::SapMachineJRE"]}'
    JBP_CONFIG_SAP_MACHINE_JRE: '{ jre: { version: 17.+ }}'

This will switch to using SAP Machine JRE. If you only specify JBP_CONFIG_SAP_MACHINE_JRE without changing JBP_CONFIG_COMPONENTS OpenJdkJRE will still be the used one. In the go-migration branch though if you have:

env:
    JBP_CONFIG_SAP_MACHINE_JRE: '{ jre: { version: 17.+ }}'

the JRE type will be switched to SAP Machine JRE without taking in concern JBP_CONFIG_COMPONENTS.