Rollup node: augment health RPC with relevant data to assess if running correctly

What

This MR adds data to the rollup node /health RPC to assess if it is currently operating correctly. This now includes:

• degraded to indicate if it is running in degraded mode
• l1.connection to indicate the connection status to the L1 node ("connected", "reconnecting", or "disconnected")
• l1.blocks_late for the number of blocks the rollup node needs to catch up on
• l1.last_seen_head for the last L1 head the rollup node was made aware of
• active_workers with a list of active workers in the rollup node
• healthy contains true if all above indicators are green.

Why

This information is useful for monitoring the rollup node on a coarse grain scale.

How

This MR exposes the necessary information about workers and the L1 connection.

Manually testing the MR

Run a rollup node and issue an RPC:

curl http://localhost:8932/health

Response should look like

{
  "healthy": true,
  "degraded": false,
  "l1": {
    "connection": "connected",
    "blocks_late": 0,
    "last_seen_head": {
      "hash": "BMCL6uQUiNn8Mm2CJoirp8K5RZ7rVuBGEog3jifLvHrpJG2fBLL",
      "level": 6026061,
      "timestamp": "2024-04-17T12:49:51Z"
    }
  },
  "active_workers": [
    [
      "publisher",
      "running"
    ],
    [
      "refutation_coordinator",
      "running"
    ],
    [
      "injector (cement)",
      "running"
    ],
    [
      "injector (publish, timeout, refute, execute_outbox_message)",
      "running"
    ]
  ]
}