Create Valkey client for artifact storage synchronization

## Overview

Implement a Valkey client to enable the storage proxy to access artifact storage configurations stored in the manager's database.

## Context

Artifact storage configurations need to be synchronized from the manager's database to the storage proxy without manual TOML file updates. This task creates the necessary Valkey client infrastructure.

## Implementation Tasks

- Create `valkey_artifact_storage` client in the storage proxy
- Configure connection pooling and timeout settings
- Implement cache key schema for artifact storage data
- Add connection health checks and retry logic

## Acceptance Criteria

- Storage proxy can read artifact storage configurations from Valkey
- Client handles connection failures gracefully
- Performance metrics are logged for cache operations

JIRA Issue: BA-3150