Feature Request: API Endpoint for Conference Information (Members, Duration, etc.)

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Currently, the Jambonz API does not offer a way to retrieve real-time information about active conferences.

I would like to propose adding a new API endpoint:

`GET /v1/Accounts/:account_sid/Conferences/:conference_sid`

This endpoint would allow querying details about a specific conference. Useful data would include:

- `conference_sid`
- `friendly_name`
- `created_at`
- `start_time`
- `duration`
- `call_status`
- `members_count`
- `members[]` (array of member objects), each containing:
- `call_sid`
- `joined_at`
- `muted`
- `hold`
- `caller_number`
- `callee_number`

While we do receive some data via the `Conference Status` webhook, there is currently no way to retrieve this information on-demand through the API.

### Example

```json
{
"conference_sid": "conf:9351f46a-678c-43f5-b8a6-d4eb58d131af:abc123456789",
"friendly_name": "abc123456789",
"created_at": "2025-06-25T08:59:50Z",
"start_time": "2025-06-25T09:00:00Z",
"duration": 1260,
"call_status": "active",
"members_count": 2,
"members": [
{
"call_sid": "5278616e-cc37-123e-5e92-02be6fb71d05",
"joined_at": "2025-06-25T09:01:05Z",
"muted": false,
"hold": false,
"caller_number": "+31101234567",
"callee_number": "+31612345678"
},
{
"call_sid": "9351f46a-678c-43f5-b8a6-d4eb58d131af",
"joined_at": "2025-06-25T09:02:10Z",
"muted": true,
"hold": false,
"caller_number": "+31101234568",
"callee_number": "+31687654321"
}
]
}
```

Start by locating the existing Conference Status webhook handling and REST API route definitions in jambonz-api-server. Compare the available conference data with the proposed GET endpoint fields, then define and test behavior for the conference details and members response described in the issue.

Written by the indexing model from the issue text.