[DOCS] Add request body param descriptions for move to step (#56560) (#56645)

Author: debadair

docs/reference/ilm/apis/move-to-step.asciidoc

@@ -47,6 +47,58 @@ an unexpected step into the next step.
 
 include::{docdir}/rest-api/common-parms.asciidoc[tag=timeoutparms]
 
+[role="child_attributes"]
+[[ilm-move-to-step-request-body]]
+==== {api-request-body-title}
+
+`current_step`::
+(Required, object)
++
+.Properties of `current_step`
+[%collapsible%open]
+====
+`phase`::
+(Required, string)
+The name of the current phase.
+Must match the phase as returned by the <<ilm-explain-lifecycle, explain>> API.
+
+`action`::
+(Required, string)
+The name of the current action. 
+Must match the action as returned by the <<ilm-explain-lifecycle, explain>> API.
+
+`name`::
+(Required, string)
+The name of the current step. 
+Must match the step as returned by the <<ilm-explain-lifecycle, explain>> API.
+If {ilm-init} encounters a problem while performing an action, 
+it halts execution of the policy and transitions to the `ERROR` step.
+If you are trying to advance a policy after troubleshooting a failure, 
+you specify this `ERROR` step as the current step. 
+For more information, see <<index-lifecycle-error-handling, {ilm-init} error handling>>.
+
+====
+
+`next_step`::
+(Required, object)
++
+.Properties of `next_step`
+[%collapsible%open]
+====
+`phase`::
+(Required, string)
+The name of the phase that contains the action you want to perform or resume.
+
+`action`::
+(Required, string)
+The name action you want to perform or resume. 
+
+`name`::
+(Required, string)
+The name of the step to move to and execute. 
+
+====
+
 [[ilm-move-to-step-example]]
 ==== {api-examples-title}