mgr/telemetry: add command to list all collections

mgr/telemetry: add command to list all collections

List all collections, their current enrollment state, status, default,
and description, with:

$ ceph telemetry collection ls

NAME                  ENROLLED    STATUS    DEFAULT    DESC
basic_base            TRUE        ON        ON         Basic information about the cluster (capacity, number and type of daemons, version, etc.)
basic_mds_metadata    TRUE        ON        ON         MDS metadata
crash_base            TRUE        ON        ON         Information about daemon crashes (daemon type and version, backtrace, etc.)
device_base           TRUE        ON        ON         Information about device health metrics
ident_base            TRUE        OFF       OFF        User-provided identifying information about the cluster
perf_perf             TRUE        OFF       OFF        Information about performance counters of the cluster

Please note:

NAME:
=====
Collection name; prefix indicates the channel the collection belongs to.

ENROLLED:
=========
Signifies the collections that were available in the module when the
user last opted-in to telemetry. Please note: Even if a collection is
'enrolled', its metrics will be reported only if its channel is enabled.

STATUS:
=======
Indicates whether the collection metrics are reported; this is
determined by the status (enabled / disabled) of the channel the
collection belongs to, along with the enrollment status of the
collection.

DEFAULT:
========
The default status (enabled / disabled) of the channel the collection
belongs to.

DESC:
=====
Collection description.

Signed-off-by: Yaarit Hatuka <yaarit@redhat.com>