Explorer API reports proxy contracts incorrectly

🐛 Bug Report

📝 Description

The explorer API incorrectly reports that a proxy smart contract isn't a proxy.

Online block explorer reports that a proxy smart contract is a proxy:
https://explorer.zksync.io/address/0x5A7d6b2F92C77FAD6CCaBd7EE0624E64907Eaf3E#contract

But the explorer API reports that the same smart contract is NOT a proxy:
https://block-explorer-api.mainnet.zksync.io/api?module=contract&action=getsourcecode&address=0x5A7d6b2F92C77FAD6CCaBd7EE0624E64907Eaf3E

            "Proxy": "0",
            "Implementation": "",

🔄 Reproduction Steps

1. Search for a proxy smart contract in the online explorer (https://explorer.zksync.io/). The explorer will show that the contract is a proxy.
2. Search for the same smart contract via the API (https://block-explorer-api.mainnet.zksync.io/api). The response will indicate that the same contract is not a proxy.

🤔 Expected Behavior

The API response should indicate that the proxy smart contract is a proxy ("Proxy": "1"). It should also return the address of the implementation contract ("Implementation").

😯 Current Behavior

The API response indicates that the proxy smart contract is NOT a proxy ("Proxy": "0"). It also doesn't return any implementation contract address ("Implementation": "").