Add note about base_path and ECE to the snapshot repository docs (#83526)

Elastic Cloud Enterprise (ECE) shares snapshot repositories across multiple deployments. As a result, the `base_path` is generated by ECE, and the `base_path` setting is not allowed.  This PR adds a note to the S3, Azure, and GCS snapshot repository docs.

docs/reference/snapshot-restore/repository-azure.asciidoc

@@ -158,6 +158,10 @@ The Azure repository supports following settings:
 
     Specifies the path within container to repository data. Defaults to empty
     (root directory).
++
+NOTE: Don't set `base_path` when configuring a snapshot repository for {ECE}.
+{ECE} automatically generates the `base_path` for each deployment so that
+multiple deployments may share the same bucket.
 
 `chunk_size`::
 

docs/reference/snapshot-restore/repository-gcs.asciidoc

@@ -227,6 +227,10 @@ The following settings are supported:
 
     Specifies the path within bucket to repository data. Defaults to
     the root of the bucket.
++
+NOTE: Don't set `base_path` when configuring a snapshot repository for {ECE}.
+{ECE} automatically generates the `base_path` for each deployment so that
+multiple deployments may share the same bucket.
 
 `chunk_size`::
 

docs/reference/snapshot-restore/repository-s3.asciidoc

@@ -276,6 +276,10 @@ bucket naming rules].
     Specifies the path to the repository data within its bucket. Defaults to an
     empty string, meaning that the repository is at the root of the bucket. The
     value of this setting should not start or end with a `/`.
++
+NOTE: Don't set `base_path` when configuring a snapshot repository for {ECE}.
+{ECE} automatically generates the `base_path` for each deployment so that
+multiple deployments may share the same bucket.
 
 `chunk_size`::