Merge branch 'js/trace2-session-id'

The transport layer was taught to optionally exchange the session
ID assigned by the trace2 subsystem during fetch/push transactions.

* js/trace2-session-id:
  receive-pack: log received client session ID
  send-pack: advertise session ID in capabilities
  upload-pack, serve: log received client session ID
  fetch-pack: advertise session ID in capabilities
  transport: log received server session ID
  serve: advertise session ID in v2 capabilities
  receive-pack: advertise session ID in v0 capabilities
  upload-pack: advertise session ID in v0 capabilities
  trace2: add a public function for getting the SID
  docs: new transfer.advertiseSID option
  docs: new capability to advertise session IDs

diff --cc builtin/receive-pack.c
Simple merge

diff --cc send-pack.c
Simple merge

diff --cc upload-pack.c
Simple merge