Update default Jenkins version

[Jonny-vb]

Update default Jenkins version for Docker iamges.

Important for Windows images as only a single tag is built for it based off the default version and the existing used tag now has a Stored XSS vulnerability

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[MarkEWaite]

While this change is not harmful, I believe it is not required.

The build process in production environments always passes a JENKINS_VERSION and a JENKINS_SHA for the container image being built. We don't rebuild old container images, but rely on the regular pace of Jenkins releases to deliver new containers with new Jenkins versions.

[Jonny-vb]

While this change is not harmful, I believe it is not required.

The build process in production environments always passes a JENKINS_VERSION and a JENKINS_SHA for the container image being built. We don't rebuild old container images, but rely on the regular pace of Jenkins releases to deliver new containers with new Jenkins versions.

This is true for linux based images, but not the windows based unfortunately - I should have linked my old issue covering this: #1490