Java8 support deprecated

[edporras]

@kawas44 @m-faucon @jeremy-lc @iomonad

Should we bump to 11 or go ahead and go beyond?

[iomonad]

I guess there is no specific reason to stick with Java 8? At least the old artifacts were built with Java 8, and the changelog could specify that newer releases are now built with and require at least Java 11.

[kawas44]

https://cloud.google.com/dataflow/docs/support/beam-runtime-support?hl=fr

Java 8 is still officially supported, let's wait for Beam 3 and follow Dataflow Java support.