fix: store configs (#2593)

# What does this PR do?
https://github.com/meta-llama/llama-stack/pull/2490 broke postgres_demo,
as the config expected a str but the value was converted to int.

This PR:
1. Updates the type of port in sqlstore to be int
2. template generation uses `dict` instead of `StackRunConfig` so as to
avoid failing pydantic typechecks.
3. Adds `replace_env_vars` to StackRunConfig instantiation in
`configure.py` (not sure why this wasn't needed before).

## Test Plan
`llama stack build --template postgres_demo --image-type conda --run`

docs/source/providers/vector_io/inline_faiss.md

@@ -44,7 +44,6 @@ more details about Faiss in general.
 ```yaml
 kvstore:
   type: sqlite
-  namespace: null
   db_path: ${env.SQLITE_STORE_DIR:=~/.llama/dummy}/faiss_store.db
 
 ```

docs/source/providers/vector_io/inline_meta-reference.md

@@ -15,7 +15,6 @@ Meta's reference implementation of a vector database.
 ```yaml
 kvstore:
   type: sqlite
-  namespace: null
   db_path: ${env.SQLITE_STORE_DIR:=~/.llama/dummy}/faiss_store.db
 
 ```

docs/source/providers/vector_io/inline_milvus.md

@@ -19,7 +19,6 @@ Please refer to the remote provider documentation.
 db_path: ${env.MILVUS_DB_PATH:=~/.llama/dummy}/milvus.db
 kvstore:
   type: sqlite
-  namespace: null
   db_path: ${env.SQLITE_STORE_DIR:=~/.llama/dummy}/milvus_registry.db
 
 ```