feat(Weaviate): Enforce capitalized index name

[edwinjosechittilappilly]

• Add get_valid_index_name method to ensure index name is capitalized
• Update index_name input with info about capitalization requirement
• Implement capitalization check before creating vector store

Ref: https://forum.weaviate.io/t/feature-or-bug-first-letter-of-class-name-gets-capitalized/1203