Update error thrown to users when the fallback keyper is not available

[ylembachar]

Update the error handling when the fallback keyper is unreachable. Currently, the API returns a 500 Internal Server Error with a low-level message that exposes the keyper’s IP address and connection failure details.

Error processing vote for identity 0x0808c3d6a8c4b0d44e39d5cbe1672be0e95cba638a755ec8679249039d0e6205: Error: API request failed with status 500: {"description":"failed to get decryption key for eon 11 and identity 0x0808c3d6a8c4b0d44e39d5cbe1672be0e95cba638a755ec8679249039d0e6205 from keyper: Get \"http://[IP_REDACTED]:3000/v1/decryptionKey/11/0x0808c3d6a8c4b0d44e39d5cbe1672be0e95cba638a755ec8679249039d0e6205\": dial tcp [IP_REDACTED]:3000: connect: connection refused","statusCode":500}