Improve decoding of JSON responses.

[cyriltovena]

Improves frontend allocation by using another json parser for streams.

This also try to use a Bytes() function if available when reading the body to avoid a copy. (This needs to be added to cortex too)

❯ benchcmp  before.txt after.txt8
benchmark                        old ns/op     new ns/op     delta
Benchmark_CodecDecodeLogs-16     9692959       6406357       -33.91%

benchmark                        old allocs     new allocs     delta
Benchmark_CodecDecodeLogs-16     124103         39037          -68.54%

benchmark                        old bytes     new bytes     delta
Benchmark_CodecDecodeLogs-16     6497881       2161604       -66.73%

Signed-off-by: Cyril Tovena cyril.tovena@gmail.com

[dannykopping]

Looks great! Left a couple comments.

[sandeepsukhani]

Nice work Cyril! Changes LGTM modulo comments by Danny!