Provide information about available/used resources for the user's namespace

[skabashnyuk]

Is your task related to a problem? Please describe.

Now when we have the ability to provide a list of namespaces available for the user to create a workspace, it would be nice
to provide also information about available/used resources for the user's namespace.

Describe the solution you'd like

Namespace API should provide information about available/used resources

• CPU
• Memory
• PV
• Secrets

Describe alternatives you've considered

n/a

Additional context

 oc describe quota object-counts                                                                          
Name:                   object-counts
Namespace:              skabashn-che
Resource                Used  Hard
--------                ----  ----
persistentvolumeclaims  1     2
replicationcontrollers  0     20
secrets                 18    20
services                0     15

Name:       compute-resources
Namespace:  skabashn-che
Scopes:     NotTerminating
 * Matches all pods that do not have an active deadline. These pods usually include long running pods whose container command is not expected to terminate.
Resource       Used  Hard
--------       ----  ----
limits.cpu     0     16
limits.memory  0     8Gi

[sleshchenko]

duplicates #13504