Add indicator service details to health API documentation. (#87712)

This PR adds listings of all the current details that can be returned from the implemented 
Health Indicator Services. Response details are unique to each indicator and describe the 
state of the system that the indicator is basing its health decisions on.

Co-authored-by: Andrei Dan <andrei.dan@elastic.co>

docs/reference/health/health.asciidoc

@@ -205,7 +205,7 @@ for health status set `explain` to `false` to disable the more expensive analysi
 `details`::
     (Optional, object) An object that contains additional information about the cluster that
     has lead to the current health status result. This data is unstructured, and each
-    indicator may return a unique set of details. Details will not be calculated if the
+    indicator returns <<health-api-response-details, a unique set of details>>. Details will not be calculated if the
     `explain` property is set to false.
 
 `impacts`::
@@ -260,6 +260,123 @@ for health status set `explain` to `false` to disable the more expensive analysi
 =====
 ====
 
+[role="child_attributes"]
+[[health-api-response-details]]
+==== Indicator Details
+
+Each health indicator in the health api returns a set of details that further explains the state of the system. The
+details have contents and a structure that is unique to each indicator.
+
+[[health-api-response-details-master-is-stable]]
+===== master_is_stable
+
+`current_master`::
+    (object) Information about the currently elected master.
++
+.Properties of `current_master`
+[%collapsible%open]
+====
+`node_id`::
+    (string) The node id of the currently elected master, or null if no master is elected.
+
+`name`::
+    (string) The node name of the currently elected master, or null if no master is elected.
+====
+
+`recent_masters`::
+    (Optional, array) A list of nodes that have been elected or replaced as master in a recent
+    time window. This field is present if the master
+    is changing rapidly enough to cause problems, and also present as additional information
+    when the indicator is `green`.
++
+.Properties of `recent_masters`
+[%collapsible%open]
+====
+`node_id`::
+    (string) The node id of a recently active master node.
+
+`name`::
+    (string) The node name of a recently active master node.
+====
+
+`exception_fetching_history`::
+    (Optional, object) Master history is requested from the most recently elected master node for diagnosis purposes.
+    If fetching this remote history fails, the exception information is returned in this detail field.
++
+.Properties of `exception_fetching_history`
+[%collapsible%open]
+====
+`message`::
+(string) The exception message for the failed history fetch operation.
+
+`stack_trace`::
+(string) The stack trace for the failed history fetch operation.
+====
+
+[[health-api-response-details-shards-availability]]
+===== shards_availability
+
+`unassigned_primaries`::
+    (int) The number of primary shards that are unassigned for reasons other than initialization or relocation.
+
+`initializing_primaries`::
+    (int) The number of primary shards that are initializing or recovering.
+
+`creating_primaries`::
+    (int) The number of primary shards that are unassigned because they have been very recently created.
+
+`restarting_primaries`::
+    (int) The number of primary shards that are relocating because of a node shutdown operation.
+
+`started_primaries`::
+    (int) The number of primary shards that are active and available on the system.
+
+`unassigned_replicas`::
+    (int) The number of replica shards that are unassigned for reasons other than initialization or relocation.
+
+`initializing_replicas`::
+    (int) The number of replica shards that are initializing or recovering.
+
+`restarting_replicas`::
+    (int) The number of replica shards that are relocating because of a node shutdown operation.
+
+`started_replicas`::
+    (int) The number of replica shards that are active and available on the sysetm.
+
+
+[[health-api-response-details-repository-integrity]]
+===== repository_integrity
+
+`total_repositories`::
+    (Optional, int) The number of currently configured repositories on the system. If there are no repositories
+    configured then this detail is omitted.
+
+`corrupted_repositories`::
+    (Optional, int) The number of repositories on the system that have been determined to be corrupted. If there are
+    no corrupted repositories detected, this detail is omitted.
+
+`corrupted`::
+    (Optional, array of strings) If corrupted repositories have been detected in the system, the names of up to ten of
+    them are displayed in this field. If no corrupted repositories are found, this detail is omitted.
+
+[[health-api-response-details-ilm]]
+===== ilm
+
+`ilm_status`::
+    (string) The current status of the Indexing Lifecycle Management feature. Either `STOPPED`, `STOPPING`, or `RUNNING`.
+
+`policies`::
+    (int) The number of index lifecycle policies that the system is managing.
+
+[[health-api-response-details-slm]]
+===== slm
+
+`slm_status`::
+    (string) The current status of the Snapshot Lifecycle Management feature. Either `STOPPED`, `STOPPING`, or `RUNNING`.
+
+`policies`::
+    (int) The number of snapshot policies that the system is managing.
+
 [[health-api-example]]
 ==== {api-examples-title}