Create endpoint to proxy Goldsky requests

[bagelface]

Description 🗒️

Currently Goldsky requests are made by frontend components which exposes the key to the public. We want to create a Next API endpoint through which we can proxy requests so that the API key is not exposed.

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Details 🏗️

Currently we are using NEXT_PUBLIC_GOLDSKY_BASE_API_URL. Instead we need to make this environment variable private GOLDSKY_BASE_API_URL and accessible only to the backend so that it is not exposed to the public. It would also be smart to rotate the API key since it has been public in production since the creation of this issue.

See TODO comment for context:

gnars-frontend/packages/webapp/.env.example

Line 18 in f54cc20

#TODO: implement and actually make private (ignore for now)

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Acceptance Criteria ☑️

1. All of the changes described in the "Details" section above are implemented and tested.
2. Code is clear, clean, and properly documented.
3. UI changes are sensible and non-regressive.