feat: Create an endpoint to fetch dynamic system configuration variables

[AlAfiz]

Description

The frontend needs to know certain global variables (like the current default slippage, supported networks, or maintenance mode status) immediately upon loading.
Hardcoding these in the frontend means we have to deploy a new React build every time a parameter changes.
We need a /api/v1/config endpoint that returns a JSON object containing these global system settings.
This allows us to control the frontend behavior entirely from the backend environment variables.

Requirements

• Create a GET route at /api/v1/config.
• Construct a JSON payload containing: defaultSlippage, maxTradeSize, maintenanceMode, and supportedNetworks.
• Populate these values using either .env variables or static defaults.
• Ensure the route returns a fast 200 OK response with caching enabled.

[Kevin737866]

@Kevin737866 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi. Can I work on this? Thanks

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