[FEAT] Chainlink.sol: add addAddress function

Description
Hello,

would it make sense to have a function that allows adding an address parameter to the request?

maybe something like

function addAddress(
    Request memory self,
    string memory key,
    address value
  ) internal pure {
    self.buf.encodeString(key);
    self.buf.encodeBytes(abi.encode(value));
  }

Motivation
Make it easier for users to add addresses (abstract the internal implementation from them). Also to have one unified approach. I found 2 ways of handling addresses (see Justification ) and maybe there are other approaches as well. IMHO, having unified approaches are more maintenable on the long run

Justification
Provide a unified approach for users. I've tried 2 methods of passing addresses:

• Parsing from address to string using Openzeppelin Strings utils. : req.add('address1',Strings.toHexString(uint256(uint160(msg.sender)), 20));
• abi.encode : req.addBytes('address2',abi.encode(msg.sender));

The 1st method doesn't require any work from the node operator (except cbor decoding). The 2nd method requires an extra abi decoding:

decode [type="ethabidecode"
        abi="address address"
        data="$(decode_cbor.address)"]

IMHO, I would prefer the second method as it clears for everyone that we are handling addresses.

Start in Chainlink.sol and compare the proposed addAddress helper with the existing addBytes usage shown in the issue. Check how request parameters are encoded and confirm that callers can pass an address through one unified helper using the described ABI encoding. Done means the helper is available with the requested signature and its encoded address can be consumed like the existing request values.