feat: ini2 parser

[lucix-aws]

Replace the legacy, undocumented, and unmaintainable shared config parser with a vastly simplified implementation.

Parse failures (unrecognized tokens) will now silently be ignored rather than dropping the entire profile, and the implementation is much more lenient in general.

I've included the benchmarks provided courtesy of @krousey in #2353 and we actually observe a performance boost from this reimplementation:

old:

goos: darwin
goarch: amd64
pkg: github.com/aws/aws-sdk-go-v2/config
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkLoadProfile1-12           15345             80243 ns/op
BenchmarkLoadProfile10-12           4615            244160 ns/op
BenchmarkLoadProfile100-12           673           1832922 ns/op
BenchmarkLoadProfile1000-12           69          16511466 ns/op
PASS
ok      github.com/aws/aws-sdk-go-v2/config     11.801s                               

new:

goos: darwin                                                    
goarch: amd64                                                   
pkg: github.com/aws/aws-sdk-go-v2/config                        
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz                   
BenchmarkLoadProfile1-12           17833             68068 ns/op
BenchmarkLoadProfile10-12           9366            117720 ns/op
BenchmarkLoadProfile100-12          1878            614622 ns/op
BenchmarkLoadProfile1000-12          219           5464137 ns/op
PASS                                                            
ok      github.com/aws/aws-sdk-go-v2/config     8.942s