This method is only needed to migrate between store.FileStore and
tpm.tpmStore. We can make a runtime type assertion instead of
implementing an unused method for every platform.
Updates #15830
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
Add a new `--encrypt-state` flag to `cmd/tailscaled`. Based on that
flag, migrate the existing state file to/from encrypted format if
needed.
Updates #15830
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>