[8u, 11u] Wiki Page updates

[Langer, Christoph]

Hi,

I have updated the Wiki Pages for both, jdk11u and jdk8u so that they look consistent.

JDK8u: https://wiki.openjdk.java.net/display/jdk8u
JDK11u: https://wiki.openjdk.java.net/display/JDKUpdates/JDK11u

I have written some sentences about processes and infrastructure, covering also the push approval process. Furthermore, I've added the upcoming release dates and links to the JBS filters.

Please review this documentation, whether it's correct in content and also whether it's understandable. Thanks in advance for any feedback.

Best regards
Christoph