feat: add close method for Cassandra (#2961)

Signed-off-by: Alexandre Liberato <alexandreliberato@mailfence.com>
Signed-off-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>
Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

state/cassandra/cassandra.go

@@ -326,3 +326,14 @@ func (c *Cassandra) GetComponentMetadata() map[string]string {
 	metadata.GetMetadataInfoFromStructType(reflect.TypeOf(metadataStruct), &metadataInfo, metadata.StateStoreType)
 	return metadataInfo
 }
+
+// Close the connection to Cassandra.
+func (c *Cassandra) Close() error {
+	if c.session == nil {
+		return nil
+	}
+
+	c.session.Close()
+
+	return nil
+}