Move Streaming to Finnhub

[bfalls]

Description:

As a developer,
I want to replace the current WebSocket streaming integration from Twelve Data with Finnhub, so that we can support real-time streaming for more symbols beyond just AAPL on the free tier.

Acceptance Criteria:

• The current WebSocket implementation using Twelve Data is removed or disabled. Consider using an adapter pattern for this so other services could be used in the future.
• A new WebSocket client is implemented to connect to Finnhub’s real-time price stream.
• The service gracefully handles subscription errors (e.g., invalid symbols).
• The updated implementation supports multiple valid stock symbols, verified against Finnhub’s limitations.
• Environment variables or SSM parameters are used to securely store and access the Finnhub API key.
• The deployment script is updated if needed to reflect the API change.
• Relevant logs and monitoring are added or updated to track connection and subscription status.
• The change is verified locally or in production with at least 3 different symbols (e.g., AAPL, TSLA, MSFT).

Notes:

• Twelve Data’s free tier currently allows WebSocket streaming for only AAPL, limiting broader usage.
• Finnhub’s free tier supports streaming for multiple symbols, making it better suited for our app’s real-time data needs.