Create descriptor-based wallet by default if above bitcoin v21.0+

[sandipndev]

When we launch the bitcoind process, the default wallet being created enables descriptor mode.

[sandipndev]

Waiting for PR RCasatta/rust-bitcoincore-rpc#1 to be merged for this to go through.

[RCasatta]

Based on the results from the CI, I think we may need to have Some(true) only on bitcoind >=0.21

something like:

let desc_wallet = if cfg!(any(feature = "22_0", feature = "0_21_1",  feature = "0_21_0")) {
   Some(true)
}
else {
   None
}

[notmandatory]

Based on the results from the CI, I think we may need to have Some(true) only on bitcoind >=0.21

Agreed, but maybe invert the logic to check if cfg!(not(any(feature = "0_20_1" .... etc., it's a bit longer but then we won't need to update this line every time a new version of core is added.

[RCasatta]

CI is reliably failing for: 0_20_1, 0_20_0, 0_19_1, 0_19_0. I think because the number of arguments of create_wallet changed (and I think master is working because None is accepted)

We may want to feature gate the call to create_wallet according to the version, but I am not sure even considering that now that https://github.com/rust-bitcoin/rust-bitcoincore-rpc finally shipped with rust-bitcoin: 0.27 I would like to go back to use that dep instead of our custom one.

@sandipndev instead of needing this in your code could you create a new wallet with descriptor_wallet true instead of changing the default?