add index naming note to clarify

Author: Lorina Poland (polandll); Reviewed by Mick Semb Wever (mck) - no ticket

doc/modules/cassandra/pages/developing/cql/indexing/sai/_sai-create.adoc

@@ -3,6 +3,8 @@
 
 To create an SAI index, you must define the index name, table name, and column name for the column to be indexed.
 
+include::cassandra:partial$index-naming.adoc[]
+ 
 To create a simple SAI index:
 
 [source, language-cql]

doc/modules/cassandra/pages/getting-started/sai-quickstart.adoc

@@ -40,6 +40,8 @@ Use xref:reference/cql-commands/create-custom-index.adoc[CREATE CUSTOM INDEX] co
 include::cassandra:example$CQL/sai/cyclist_semi_pro_sai_indices.cql[tag=createQuickStartIndices]
 ----
 
+include::cassandra:partial$index-naming.adoc[]
+
 Let's take a look at the description of the table and its indexes:
 [tabs]
 ====

doc/modules/cassandra/pages/reference/cql-commands/create-custom-index.adoc

@@ -54,6 +54,8 @@ index_name::
 Optional identifier for index.
 If no name is specified, the default used is `<table_name>\_<column_name>\_idx`.
 Enclose in quotes to use special characters or to preserve capitalization.
++
+include::cassandra:partial$index-naming.adoc[]
 
 column_name::
 The name of the table column on which the SAI index is being defined.

doc/modules/cassandra/pages/reference/cql-commands/create-index.adoc

@@ -75,6 +75,8 @@ SAI returns `InvalidRequestException` if you try to define an index on a column
 Enclose in quotes to use special characters or preserve capitalization.
 If no name is specified, {product} names the index as `<table_name>\_<column_name>\_idx`.
 
+include::cassandra:partial$index-naming.adoc[]
+
 | keyspace_name
 | Name of the keyspace that contains the table to index.
 If no name is specified, the current keyspace is used.

doc/modules/cassandra/partials/index-naming.adoc

@@ -0,0 +1,6 @@
+[WARNING]
+====
+Index names are unique per keyspace.
+The index name must be a unique identifier for the index for each table within a keyspace.
+This requirement is true for both vector and non-vector indexes.
+====