Let user select the type of shell in `shell` filters

[Nusiq]

Currently it goes through the list {"powershell", "-command"}, {"cmd", "/k"}, {"bash", "-c"}, {"sh", "-c"}} and picks whichever is available first (so... always powershell on windows I guess).

[stirante]

Original cmd is being slowly phased out on windows iirc. Also I intentionally did not add a way to specify shell, because that would make it platform dependant. One way to fix it would be to make shell filter accept unix script and windows script separately and choosing the shell separately as well

[Nusiq]

Shell commands are different in different shells so it's platform dependent anyways.