Adds a new get_key function which generates
a new key and returns the public key,
private key and all script and address types.
Partial backport of Core [[https://github.com/bitcoin/bitcoin/pull/14886 | PR14886]]
https://github.com/bitcoin/bitcoin/pull/14886/commits/7c99614b40301daba5e526c6e3ab281965e869c6
Depends on D6051 and D6081