[RFE] Add new omc etcd subcommand for the etcd object count in newer must-gathers

[oarribas]

In newer must-gather versions (4.17.5+ and 4.16.27+ for now), there is a new file in the etcd_info subdirectory, that includes the etcd object count (check RFE-5765 [1] and the PR [2] for additional information).

The file is a key-value json with object_kind: number_of_objects, like:

$ jq . etcd_info/object_count.json
{
  "events": "1242",
  "secrets": "635",
  "configmaps": "525",
[...]

This RFE is to include a new omc etcd objects sub-command (or different name) to show that information if the above file exists,as in many cases it could help identifying an issue due to big amount of any object. The default command could show only the top-10 object count.

[1] https://issues.redhat.com/browse/RFE-5765
[2] openshift/must-gather#435