Export bitcoin xpub / provide xpub with wallet connect

[shivaenigma]

Various bitcoin wallets are currently providing xpub. There are various use cases for an xpub:

1. Watch only wallets
2. Accounting
3. Non custodial merchants services like BTCPay and Blockonomics require extended public key to help merchants receive payments directly to wallet without compromising funds secruity

It is true that UX wise xpub sounds too technical and copying/pasting xpub seems like this a big task !
Thus I suggest to include xpub information in wallet connect endpoint so that connecting services can directly pull this from the wallet and make the process easier for the user

[314159265359879]

related discussion: https://forum.stacks.org/t/developing-a-non-custodial-payment-gateway-for-stx/15971

[vinlim]

I have proposed to introduce getXpub RPC method with this PR #4958 to support this. Would love to hear comments on the approach.