Dropping single user support

[l0rd]

@riuvshin started a discussion on che-dev mailing list proposing that we drop the support for Che single user (Che multi user would be the only option).

In this epic we want to track the tasks needed to drop single user support.

• 1. adapt minishift addon to support multi-user Che Che addon: add support for multi user Che minishift/minishift#2746
• 2. find an alternative to keycloak for local development (e.g. a lightweight OIDC provider) Look at Keycloak lightweight alternatives for local development #10998
• 3. provide details on the performances (disk/network/RAM/CPU/boot time) and get PM signoff
• 4. drop single user support from deployment scripts/tools:
  • che CLI
  • ocp.sh
  • minishift addon
  • helm chart
• 5. Drop support for single user Che in build / CI / QE (Drop single-user support from E2E selenium tests of Eclipse Che #10999)
• 6. Remove single user Che related modules
• 7. Remove single user references in documentation

[dmytro-ndp]

@l0rd: please, take into consideration E2E selenium tests as well #10999

[che-bot]

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