DOC-11735: Correct HTTP verb (#770)

Author: ElliotFrancisHunter

modules/ROOT/pages/_partials/howto/how-to-use-xattrs-for-access-grants.adoc

@@ -58,7 +58,7 @@ CURL::
 --
 [source, json]
 ----
-curl -X PUT 'http://localhost:4985/hotels/_config' \
+curl -X POST 'http://localhost:4985/hotels/_config' \
 --header 'Accept: application/json' \
 --header 'Content-Type: application/json' \
 --data-raw '{
@@ -76,7 +76,7 @@ HTTP::
 
 [source, http]
 ----
-PUT /hotels/_config HTTP/1.1
+POST /hotels/_config HTTP/1.1
 Host: http://localhost:4985
 Accept: application/json
 Content-Type: application/json