packages: Add a new FreeBSD-shell package

[ivy]

Summary

Add a shell package which contains /bin/sh along with all the shell
utilities which are currently installed in FreeBSD-runtime.

This moves a large number of executables out of FreeBSD-runtime,
making it more suitable for building small jails and container
images that don't require a shell.

The remaining executables in runtime are mainly system utilities
not typically used in shell scripts, which we'll probably want to
move to their own package.

MFC after: never

[ivy]

also move md5, xinstall and chown

[manu]

Not sure I like that but I could be ok if people wants this. Is this package vital ?

[ivy]

In D53162#1214496, @manu wrote:

Not sure I like that but I could be ok if people wants this. Is this package vital ?

the idea behind this is support applications that need the "base FreeBSD system", as in files like /etc/services or /etc/passwd, but don't need any executables or libraries. the main target would be service jails and container running specific applications (perhaps statically linked, like Go). to do that, either we move the executables out of runtime, or we make a new package for the non-executables files, and i thought moving the executables made more sense.

yes, it should be vital, i'll fix that.