Static version number in devfile registry doc

[rkratky]

Describe the bug

The doc at https://www.eclipse.org/che/docs/che-7/administration-guide/building-custom-registry-images/#building-custom-devfile-registry-image_che lists

Ste #1 of the procedure:

$ git clone git@github.com:eclipse/che-devfile-registry.git
$ cd che-devfile-registry
$ git checkout 7.19.x

The version should be parametrized to always show the latest released version. (Or, if it already is parametrized, the value needs updating.)

Che version

• latest
• nightly
• other: please specify

Steps to reproduce

[themr0c]

Referenced in https://issues.redhat.com/browse/RHDEVDOCS-2461

[che-bot]

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