Update db init

[shixiao-coder]

This PR unlink the enable_embeddings flag with the init DB.
database initialization will always do init on Embedding related schema

[gemini-code-assist]

Code Review

This pull request refactors the database initialization in spanner_client.py to unconditionally set up the embedding schema, extracting the DDL reading and rendering logic into a new helper method. The review feedback points out a typo in the new method's name, recommends specifying the file encoding when reading the schema file, and suggests removing the now-unused enable_embeddings parameter from the initialize_database method signature.

[gmechali]

one nit plus one small question discussed in person on API enablement and the CREATE MODEL but LGTM otherwise.