Update description for `kibana_system` role

[legrego]

The description for the kibana_system role has fallen out of date with its current permission set, and should be updated to better reflect reality.

elasticsearch/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authz/store/KibanaOwnedReservedRoleDescriptors.java

Lines 671 to 677 in 3017e33

	"Grants access necessary for the Kibana system user to read from and write to the Kibana indices, "
	+ "manage index templates and tokens, and check the availability of the Elasticsearch cluster. "
	+ "It also permits activating, searching, and retrieving user profiles, "
	+ "as well as updating user profile data for the kibana-* namespace. "
	+ "Additionally, this role grants read access to the .monitoring-* indices "
	+ "and read and write access to the .reporting-* indices. "
	+ "Note: This role should not be assigned to users as the granted permissions may change between releases."

Adding Team:Security label, but I expect @elastic/kibana-security to own this. We do not have our own team label in this repo.