UploadPack: Receive and parse client session-id

UploadPack: Receive and parse client session-id

Before this change JGit did not support the session-id capability
implemented by native Git in UploadPack. This change implements
advertising the capability from the server and parsing the session-id
received from the client during an UploadPack operation.

Enable the transfer.advertisesid config setting to advertise the
capability from the server. The client may send a session-id capability
in response. If received, the value from this is parsed and available
via the getClientSID method on the UploadPack object.

This change does not add the capability to send a session-id from the
JGit client.

https://git-scm.com/docs/gitprotocol-capabilities#_session_idsession_id

Change-Id: Ib1b6929ff1b3a4528e767925b5e5c44b5d18182f
Signed-off-by: Josh Brown <sjoshbrown@google.com>