fix: add CORs headers to cache hit responses

[pirtleshell]

if CORs is enabled in the underly nginx proxy, it adds necessary CORs headers to the response.

when the proxy service finds a cache hit, it does not add any CORs related header (or any of the originally cached request's response headers). thus, on cache hits, responses that would otherwise be allowed by CORs are rejected.

as a temporary fix to this, i've added appropriate CORs headers to all responses from cache hits. long-term, some response headers should get cached with the result data.

[galxy25]

lets cache and use a (whitelisted set of) response headers from the cached response so that we return all headers needed by web clients (e.g. some browsers or extension may require a more constrained allowed origin)