Improve Che Release Process Part 3

[nickboldt]

Follows up from #17101

Process automation:

• include che-operator, che-operator PR generation, and chectl in overall release script

• Move Che release workflow from Centos CI Move Che release workflow from Centos CI #17857 (mostly done, continued in Improve Che Release Process Part 4 #19007)

• generated PRs for plugin registry should remove all but the latest plugins (instead of including multiple copies of machine-exec and theia) generated PRs for plugin registry should remove all but the latest plugins (instead of including multiple copies of machine-exec and theia) #18596

• generate branches in https://github.com/eclipse/che-jwtproxy Generate branches every sprint for jwtproxy #17743

• generate branches in https://github.com/che-incubator/kubernetes-image-puller Generate branches every sprint for kubernetes image puller #17742

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Runtime & PR testing:

• Verify that plugin images referenced in the plugin registry actually exist in Quay Verify that plugin images referenced in the plugin registry actually exist in Quay #16501

• stop release if required artifacts are not found (eg., plugin-registry 7.14.2 container not available in quay, so don't start releasing che server)

• fail during release, if snapshot versions found, eg.,

$➔ count=$(grep -R "SNAPSHOT" * | grep pom.xml | wc -l); if [[ $count -gt 0 ]]; then echo "[ERROR] Found $count files which use a SNAPSHOT version. Cannot proceed with release."; exit 1; fi
[ERROR] Found 303 files which use a SNAPSHOT version. Cannot proceed with release.

• replace manual testing of deployment on openshift w/ PR validation check that triggers CRW QE Jenkins automated e2e test to deploy on OCP 4.4, 3.11, 4.5, 4.3 replace manual testing of deployment on openshift w/ PR validation check that triggers CRW QE Jenkins automated e2e test to deploy on OCP 4.4, 3.11, 4.5, 4.3 #17747

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Doc:

• add more documentation covering functionality of specific usecases (e.g. skipping/rebuilding particular items from release )
  --> see items 5-6 on https://github.com/eclipse/che-release/blob/master/README.md#phase-1---automated-build-steps

• Remove VERSION file in che-docs; keep antora-playbook.yml up to date instead Remove VERSION file in che-docs; keep antora-playbook.yml up to date instead #18864

[nickboldt]

Slipping this to 7.26 and we'll ACTUALLY complete it this time :D

[nickboldt]

Continued in #19007