Add `signatureAlgorithms` argument to `Sig` class

[cgcardona]

Currently Sig defaults to Schnorr signatures which is causing a problem w/ MultiSig contracts. We need to default to ECDSA sigs and add an optional 3rd signatureAlgorithms argument to the Sig class. For example

export declare class Sig {
    keypair: ECPair;
    hashtype: number;
    sigtype: number;
    constructor(keypair: ECPair, hashtype: number, sigtype: number = 0x00);
}

[cgcardona]

Also can we make the hashtype argument optional and default to 0x01? That way there could be 3 states.

// default to 0x01 SIGHASH_ALL for hashtype and 0x00 ECDSA for sigtype
.spend(alicePK, new Sig(aliceKP))

// default to 0x00 ECDSA for sigtype
.spend(alicePK, new Sig(aliceKP, 0x01))

// explicit
.spend(alicePK, new Sig(aliceKP, 0x01, 0x00))

[cgcardona]

Let's pair program when you get to this so that we can confirm the hashtype and sigtype hex values are correct in my comment above.

Primarily we want to add a 3rd sigtype arg to the Sig constructor. We also want to make the 2nd and 3rd args optional. Ensure the 2nd arg defaults to SIGHASH_ALL and ensure the 3rd arg defaults to ECDSA

[rkalis]

Since multisigs now also support Schnorr signatures, I'd prefer being opinionated and only allowing Schnorr until there's a very strong use case for providing ECDSA support in SignatureTemplate.