cmd/tailscale/cli: print node signature in `tailscale lock status`

- Add current node signature to `ipnstate.NetworkLockStatus`;
- Print current node signature in a human-friendly format as part
  of `tailscale lock status`.

Examples:

```
$ tailscale lock status
Tailnet lock is ENABLED.

This node is accessible under tailnet lock. Node signature:
SigKind: direct
Pubkey: [OTB3a]
KeyID: tlpub:44a0e23cd53a4b8acc02f6732813d8f5ba8b35d02d48bf94c9f1724ebe31c943
WrappingPubkey: tlpub:44a0e23cd53a4b8acc02f6732813d8f5ba8b35d02d48bf94c9f1724ebe31c943

This node's tailnet-lock key: tlpub:44a0e23cd53a4b8acc02f6732813d8f5ba8b35d02d48bf94c9f1724ebe31c943

Trusted signing keys:
	tlpub:44a0e23cd53a4b8acc02f6732813d8f5ba8b35d02d48bf94c9f1724ebe31c943	1	(self)
	tlpub:6fa21d242a202b290de85926ba3893a6861888679a73bc3a43f49539d67c9764	1	(pre-auth key kq3NzejWoS11KTM59)
```

For a node created via a signed auth key:

```
This node is accessible under tailnet lock. Node signature:
SigKind: rotation
Pubkey: [e3nAO]
Nested:
  SigKind: credential
  KeyID: tlpub:6fa21d242a202b290de85926ba3893a6861888679a73bc3a43f49539d67c9764
  WrappingPubkey: tlpub:3623b0412cab0029cb1918806435709b5947ae03554050f20caf66629f21220a
```

For a node that rotated its key a few times:

```
This node is accessible under tailnet lock. Node signature:
SigKind: rotation
Pubkey: [DOzL4]
Nested:
  SigKind: rotation
  Pubkey: [S/9yU]
  Nested:
    SigKind: rotation
    Pubkey: [9E9v4]
    Nested:
      SigKind: direct
      Pubkey: [3QHTJ]
      KeyID: tlpub:44a0e23cd53a4b8acc02f6732813d8f5ba8b35d02d48bf94c9f1724ebe31c943
      WrappingPubkey: tlpub:2faa280025d3aba0884615f710d8c50590b052c01a004c2b4c2c9434702ae9d0
```

Updates tailscale/corp#19764

Signed-off-by: Anton Tolchanov <anton@tailscale.com>

0 files changed, 0 insertions, 0 deletions