Che Server http sessions leak

[skabashnyuk]

Describe the bug

During my test #13034

I've noticed that if we are not using browser client as we do for brockers, chectl, etc we
create an individual http session on tomcat side that may because of memory leak.
The goal of this task is to use a single http session after we identified the actual user. We can reuse parts of Codenvy SSO code to do that.

Che version

• latest
• nightly
• other: please specify

Steps to reproduce

multiple requests like curl http://localhost/api/user with keycloak token.

Expected behavior

Tomcat will use the same http session for all request processing.

Runtime

• kubernetes (include output of kubectl version)
• Openshift (include output of oc version)
• minikube (include output of minikube version and kubectl version)
• minishift (include output of minishift version and oc version)
• docker-desktop + K8S (include output of docker version and kubectl version)
• other: (please specify)

Installation method

• chectl
• che-operator
• minishift-addon
• I don't know

Environment

• my computer
  • Windows
  • Linux
  • macOS
• Cloud
  • Amazon
  • Azure
  • GCE
  • other (please specify)
• other: please specify

Additional context

[skabashnyuk]

13 http sessions just to open one workspace

[mshaposhnik]

Merged in #15000