Add optional `--upstream` flag to `tailscale version` to fetch the
latest upstream release version from `pkgs.tailscale.com`. This is
useful to diagnose `tailscale update` behavior or write other tooling.
Example output:
$ tailscale version --upstream --json
{
"majorMinorPatch": "1.47.35",
"short": "1.47.35",
"long": "1.47.35-t6afffece8",
"unstableBranch": true,
"gitCommit": "6afffece8a32509aa7a4dc2972415ec58d8316de",
"cap": 66,
"upstream": "1.45.61"
}
Fixes#8669
RELNOTE=adds "tailscale version --upstream"
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
f57cc19ba2