snap: Additional verification of the Bitcoin Core snap package needed (hash missing)

[bigjoe123123]

I propose that together with each release there is SHA256 hash published of the installed client binary so people can easily run SHA256 binary files verification on their machine therefore we have better chance to avoid situations like this: https://twitter.com/LukeDashjr/status/1609937505217904642

I'm aware that people can download the Bitcoin Core source code and compile it themselves but let's face it - few people actually want to do that and the vast majority will use the binary (from some place) so let's give them a fighting chance to defend themselves in a realistic way.

[ツ]

Yes, a SHA256 file is available, see https://bitcoincore.org/en/download/