Installation guide: update content for devworkspace, in the master branch

[l0rd]

Is your task related to a problem? Please describe

Installation guide to document only instances with devworkspace.

https://www.eclipse.org/che/docs/next/administration-guide/installing-che/

Describe the solution you'd like

Installation guide: remove content for unavailable features on instances with devworkspace, in the master branch.

Here is the current list of the install guide articles with in bold the ones to update:

• supported-platforms @ibuziuk docs: Installation guide supported platforms che-docs#2284
• installing-che
  • installing-che-in-cloud
    • installing-che-on-openshift-4-using-operatorhub @ibuziuk docs: Installing Che on OpenShift 4 using OperatorHub che-docs#2299
    • installing-che-on-openshift-4-using-cli @ibuziuk [NO UPDATE NEEDED] the content is up to date:
    • https://www.eclipse.org/che/docs/next/administration-guide/using-the-chectl-management-tool/
    • https://www.eclipse.org/che/docs/next/administration-guide/installing-che-on-openshift-4-using-cli/
  • running-che-locally
    • installing-che-on-codeready-containers @ibuziuk docs: updating minikube and crc installation guides che-docs#2302
    • installing-che-on-minikube @ibuziuk docs: updating minikube and crc installation guides che-docs#2302
  • installing-che-in-a-restricted-environment @ScrewTSW @themr0c procedures: Installing Che in a restricted environment on OpenShift che-docs#2307
• advanced-configuration @l0rd
  • configuring-namespace-strategies @l0rd @themr0c procedures: Configuring workspace target namespace, Provisioning namespaces che-docs#2301
  • mounting-a-secret-as-a-file-or-an-environment-variable-into-a-container @l0rd docs: mounting volumes, secrets and configmaps for devworkspaces che-docs#2296
• uninstalling-che (add devworkspace related uninstall bits) @dkwon17 docs: update uninstallation guide che-docs#2281
  • uninstalling-che-after-operatorhub-installation-using-openshift-web-console
  • uninstalling-che-after-operatorhub-installation-using-openshift-cli
  • uninstalling-che-after-chectl-installation

[nickboldt]

Engineering ownership: deploy/prod/qe team / Nick + Tibor + Sam (@ 50%)

[pmkovar]

Cloned in Jira: https://issues.redhat.com/browse/RHDEVDOCS-3884

[nickboldt]

Note: https://www.eclipse.org/che/docs/next/administration-guide/supported-platforms/ currently states:
OpenShift Container Platform versions 3.11, 4.3, and 4.4
but should be
OpenShift Container Platform versions 4.9, 4.10 EUS

https://www.eclipse.org/che/docs/next/administration-guide/calculating-che-resource-requirements/ mentions keycloak too, which is no longer part of the deployment

[pmkovar]

Pairing engineers with writers:

• @deerskindoll x @nickboldt
• @themr0c x @ScrewTSW
• @max-cx x Sam + @dkwon17
• @Eva-Lotte x @amisevsk

[themr0c]

I believe we can close this issue and follow up in #21393 for the last bugs.