S3/Azure snapshot repo documentation wrong for "read_only"

We used to write that people should use `read_only` although it should be `readonly`.

Closes #22007.

docs/plugins/repository-azure.asciidoc

@@ -121,14 +121,14 @@ The Azure repository supports following settings:
     setting doesn't affect index files that are already compressed by default.
     Defaults to `false`.
 
-`read_only`::
+`readonly`::
 
-    Makes repository read-only. coming[2.1.0]  Defaults to `false`.
+    Makes repository read-only. Defaults to `false`.
 
 `location_mode`::
 
     `primary_only` or `secondary_only`. Defaults to `primary_only`. Note that if you set it
-    to `secondary_only`, it will force `read_only` to true.
+    to `secondary_only`, it will force `readonly` to true.
 
 Some examples, using scripts:
 

docs/plugins/repository-s3.asciidoc

@@ -240,7 +240,7 @@ The following settings are supported:
 
     Set to `true` if you want to throttle retries. Defaults to AWS SDK default value (`false`).
 
-`read_only`::
+`readonly`::
 
     Makes repository read-only. Defaults to `false`.