Adds two new headers to HTTP serve proxy:
- `Tailscale-User-Login`: Filled with requester's login name.
- `Tailscale-User-Name`: Filled with requester's display name.
These headers only get filled when the SrcAddr is associated with
a non-tagged (i.e. user-owned) node within the client's Tailnet.
The headers are passed through empty when the request originated
from another tailnet, or the public internet (via funnel).
Updates https://github.com/tailscale/tailscale/issues/6954
Signed-off-by: Sonia Appasamy <sonia@tailscale.com>
e1cdcf7708