buildscripts: simplify PSM interop Kokoro buildscripts (v1.57.x backport)#11165

sergiitk merged 1 commit intogrpc:v1.57.xgrpc/grpc-java:v1.57.xfrom

sergiitk:backport-1.57-psm-interop-common-prod-testssergiitk/grpc-java:backport-1.57-psm-interop-common-prod-testsCopy head branch name to clipboard