Create GsonPayloadAdapter to encrypt/decrypt WalletConnect payloads

[mitsinsar]

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Since serialize/deserialize adapter wasn't created for Encrypted Payload (it is commented out in MoshiPayloadAdapter line 226), we were having issues while working with encrypted payloads.

Also library forces us to use Moshi which we don't use in our project. That's why I've created GsonPayloadAdapter but we still need Moshi for FileWCSessionStore. I am planning to create another WCSessionStore that uses gson soon.