`xrpl` should be added as peerDependency to @gemwallet/api

[mojtabast]

For integrating your wallet extension, I only added @gemwallet/api but my build failed since I didn't have xrpl in my dependencies. To avoid this problem that would be great to enforce users to install xrpl by adding it as peerDependency on your package.

Error I've encountered:

../../node_modules/@gemwallet/api/_constants/payload/payload.types.d.ts:1:66 - error TS2307: Cannot find module 'xrpl' or its corresponding type declarations.

1 import { AccountSetAsfFlags, Path, SubmittableTransaction } from 'xrpl';
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