Separate drop_chunked_trailers setting for incoming and outgoing connections

[maskit]

It would be nice if drop_chunked_trailers could have different values for incoming connections (client connections) and outgoing connections (server/origin connections).

There are two ways to support this:

A) Use one setting for everything

0: Disabled on both
1: Enabled on both
2: Enabled only on incoming connections
3: Enabled only on outgoing connections

B) Use separate settings

drop_chunked_trailers = 0: Disabled on both
drop_chunked_trailers = 1: Enabled on both
drop_chunked_trailers = 2: Use separate settings

drop_chunked_trailers_in/out = 0 Disabled (if drop_chunked_trailers = 2)
drop_chunked_trailers_in/out = 1 Enabled (if drop_chunked_trailers = 2)

The suffix _in/out are used for many settings for ATS, and it's uncommon to have both suffixed one and non-suffixed one. B) would allow us to remove the non-suffixed one in the future.