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`

llama_stack/templates/llama_api/run.yaml

@@ -48,7 +48,6 @@ providers:
     config:
       persistence_store:
         type: sqlite
-        namespace: null
         db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/llama_api}/agents_store.db
       responses_store:
         type: sqlite
@@ -66,7 +65,6 @@ providers:
     config:
       kvstore:
         type: sqlite
-        namespace: null
         db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/llama_api}/meta_reference_eval.db
   datasetio:
   - provider_id: huggingface
@@ -74,14 +72,12 @@ providers:
     config:
       kvstore:
         type: sqlite
-        namespace: null
         db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/llama_api}/huggingface_datasetio.db
   - provider_id: localfs
     provider_type: inline::localfs
     config:
       kvstore:
         type: sqlite
-        namespace: null
         db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/llama_api}/localfs_datasetio.db
   scoring:
   - provider_id: basic