Fixes: #3181https://github.com/spring-projects/spring-ai/issues/3181
When using CassandraVectorStore with an invalid index name and
initializeSchema=false, the application would throw a generic
NoSuchElementException from Optional.get() with message "No value present"
when trying to access the index metadata.
Changes:
- Added explicit validation of index existence in checkSchemaValid() method
- Improved error handling in getIndexSimilarity() method to provide a clear
error message when an index doesn't exist
- Added integration test to verify proper error handling with invalid index names
Signed-off-by: Soby Chacko <soby.chacko@broadcom.com>