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/postgres-demo/postgres_demo.py

@@ -114,7 +114,7 @@ def get_distribution_template() -> DistributionTemplate:
                             provider_id="meta-reference",
                             provider_type="inline::meta-reference",
                             config=dict(
-                                service_name="${env.OTEL_SERVICE_NAME:=}",
+                                service_name="${env.OTEL_SERVICE_NAME:=\u200b}",
                                 sinks="${env.TELEMETRY_SINKS:=console,otel_trace}",
                                 otel_trace_endpoint="${env.OTEL_TRACE_ENDPOINT:=http://localhost:4318/v1/traces}",
                             ),

llama_stack/templates/postgres-demo/run.yaml

@@ -51,7 +51,7 @@ providers:
   - provider_id: meta-reference
     provider_type: inline::meta-reference
     config:
-      service_name: ${env.OTEL_SERVICE_NAME:=}
+      service_name: "${env.OTEL_SERVICE_NAME:=\u200B}"
       sinks: ${env.TELEMETRY_SINKS:=console,otel_trace}
       otel_trace_endpoint: ${env.OTEL_TRACE_ENDPOINT:=http://localhost:4318/v1/traces}
   tool_runtime: