Add wait_for_completion parameter to the documents of shrink, clone, split, open, and forcemerge APIs

[gaobinlong]

Is your feature request related to a problem? Please describe.
In PR opensearch-project/OpenSearch#6434, we introduced a new request parameter wait_for_completion for the shrink, clone, split, open, and forcemerge APIs, we need to document it.

Describe the solution you'd like
Add some description for the parameter wait_for_completion in the documents of shrink, clone, split, open, and forcemerge APIs, just like reindex API, we can refer to the description of the same parameter in reindex API's document.

[krisfreedain]

Hello @gaobinlong - I believe this issue should be moved to the https://github.com/opensearch-project/documentation-website repo (cc @hdhalter )