Setup eclipse CI integration for ibmruntimes/openj9-openjdk-jdk repo

[jdekonin]

Please can we setup CI integration for the openjdk extensions "head" repository, similar to the jdk11 setup.

copyright/line end checks
nightly builds, build/sanity/extended
PR builds for both openjdk (next) and openj9

fyi @vsebe

[vsebe]

Created PRs (compile, extended, sanity) for OpenJ9 and OpenJDK.

[vsebe]

Created build (e.g. Build-JDKnext-<platform> ) and test extended.functional(Test-extended.functional-JDKnext-<platform>), extended.system (Test-extended.system-JDKnext-<platform>), sanity.functional (Test-sanity.functional-JDKnext-<platform>) pipelines.

Note there is no groovy script available yet for testing linux x86 large heap, expecting a script named openjdk_x86-64_linux_largeHeap (see openjdk-test repository).

[vsebe]

@smlambert @llxia fyi

[llxia]

Issue is created in AdoptOpenJDK adoptium/aqa-tests#504 to add missing generic Jenkins file.

fyi, please use generic Jenkins file (not java version specific ones). For example, openjdk11_xxx will not be created.

[vsebe]

Tested PRs triggers - see #2557
Updated readme.