ProtocolV2Parser: Introduce advertise sideband-all option

ProtocolV2Parser: Introduce advertise sideband-all option

The flag enabling sideband-all is used in two places: in UploadPack
for advertisement and in the protocol parser to read it from the
request.

This leds to problems in distributed deployments where the two requests of
a fetch can go to different servers with different configurations.

Use the existing allowsidebandall to accept the sideband-all request
(and respond to it) and introduce a new "advertisesidebandall" to toggle
the advertising of the feature.

Change-Id: I892d541bc3f321606c89bad1d333b079dce6b5fa
Signed-off-by: Ivan Frade <ifrade@google.com>