Support metadata and configuration in embedded CreateCollection

[tazarov]

Problem

EmbeddedCreateCollectionRequest currently only supports name, tenant_id, database_name, and get_or_create.

Because of that, callers cannot persist collection metadata or collection configuration at creation time in embedded mode.

In chroma-go this forces metadata/configuration to live in process-local state only, so after restart the embedded runtime does not have the same settings. This also affects persistence of EF-relevant collection configuration (for example HNSW-related space/config choices) across restarts.

Reference context: amikos-tech/chroma-go PR #399

Requested change

Extend embedded create-collection API surface to accept and persist:

• collection metadata
• collection configuration (including EF-relevant collection settings)
• (optionally) schema if supported by runtime

Suggested acceptance criteria

1. EmbeddedCreateCollectionRequest includes fields for metadata and configuration.
2. Embedded runtime persists those values and returns them on subsequent GetCollection/listing paths (or provides dedicated retrieval API).
3. Values survive runtime restart when persistence is enabled.
4. Tests cover create -> restart -> get behavior for metadata/configuration persistence.