TransferConfig: Move reading advertisesid setting into TransferConfig

TransferConfig: Move reading advertisesid setting into TransferConfig

The config setting to enable advertising the session-id capability is
currently read in the ReceivePack class. This change moves it to a
common location in the TransferConfig class so that it can be reused
in other places like UploadPack. TransferConfig is also a more logical
place for the setting as it resides in the `transfer` config section.

Set the transfer.advertisesid setting to true to send the session-id
capability to the client.

Change-Id: If68ecb5e68b59f5c452a7992d02e3688b0a86747
Signed-off-by: Josh Brown <sjoshbrown@google.com>