Add pkg_config_path class method #4

Job	Run time
Make distribution using Dist::Zilla	13s
Perl 5.8 on ubuntu-latest with install-type system, dist	46s
Perl 5.8 on ubuntu-latest with install-type share, dist	40s
Perl 5.20 on ubuntu-latest with install-type system, dist	54s
Perl 5.20 on ubuntu-latest with install-type share, dist	1m 2s
Perl 5.30 on ubuntu-latest with install-type system, dist	33s
Perl 5.30 on ubuntu-latest with install-type share, dist	53s
Perl 5.34 on ubuntu-latest with install-type system, dist	47s
Perl 5.34 on ubuntu-latest with install-type share, dist	48s
Perl 5.34 on windows-latest with install-type share, dist strawberry	3m 13s
Perl 5.34 on windows-latest with install-type system, dist msys2	3m 12s
Perl 5.34 on windows-latest with install-type share, dist msys2	6m 56s
Perl 5.34 on macos-11 with install-type system, dist	52s
Perl 5.34 on macos-11 with install-type share, dist	1m 38s
	22m 27s

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