Add new parameter `tenant_name_discovery`

Add new parameter `tenant_name_discovery`

Enabling this parameter will identify user and project
names from the polled metrics [1].

These details are collected by making additional requests
to keystone service, depending upon the scale of environment,
number of projects/users and the count of metrics polled in
every iteration, enabling this could overwhelm the keystone
service.

[1] Iee5dbf09a1fd3ac571746fc66d2683eb8e6a1b27

Depends-on: https://review.opendev.org/852948
Signed-off-by: Yadnesh Kulkarni <ykulkarn@redhat.com>
Change-Id: I045c7cd7a86d0f7f97a9078cbfc74353dcff0eb8