Document spaces usage collection schema

[legrego]

#92701 introduced a new description field to the telemetry schema. This allows us to provide a description of what the field is collecting. This will help analysts using the telemetry cluster to understand what they can use those fields for and what they actually mean.

We should update our spaces plugin telemetry collection to include these fields.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)