Breaking Change: Consider updating Convert and MustConvert signature

[ccoVeille]

The idea came out here, when @c4rlo stated this

Having looked at the https://github.com/ccoVeille/go-safecast package a bit more closely

Specifically, the issue is that safecast.MustConvert takes an any argument, instead of being generic over the input type, meaning there are missed opportunities where things that could be compile-time errors are runtime errors.

maybe the go-safecast package can also be improved

Originally posted by @c4rlo in spiffe/spire#5737 (comment)

I didn't consider this idea when I created Convert then added MustConvert

• Consider adding Convert function handling all types #21 with Add Convert and support conversion from string and boolean #55
• Add Must* functions that will panic on error #20 with feat: add MustConvert #59

Important

The change should be considered as a breaking change as the signature will change