[FEAT][API] Create signal metrics job

## Description
Create a signal metrics job.
## Request

### Method
POST

### URL
/jobs/metrics/signal
### Request Parameters
| Parameter | Description | Required | example |
|---|---|---|---|
| kind | | | JobKind.signal_metrics |

### Request Body
```json
{
"parameters": {
"data_source": "my_data_source",
"signal": "my_signal"
}
}

```

## Result

### Result parameters
| Parameter | Description | Required | example |
|---|---|---|---|
| id | Id | | 123e4567-e89b-12d3-a456-426655440000 |
| kind | | | JobKind.signal_metrics |
| created_at | Created At | | 2023-05-18T10:10:10.000Z |
| status | Status | | JobStatus.pending |
| error_message | Error Message | | null |
| traceback | Traceback | | null |
| result | Result | | null |
| parameters | Parameters | | { "data_source": "my_data_source", "signal": "my_signal" } |
| current_progress | Current Progress | | null |

### Result Body
```json
{
"id": "123e4567-e89b-12d3-a456-426655440000",
"kind": "signal_metrics",
"created_at": "2023-05-18T10:10:10.000Z",
"status": "pending",
"error_message": null,
"traceback": null,
"result": null,
"parameters": {
"data_source": "my_data_source",
"signal": "my_signal"
},
"current_progress": null
}
```

## Example Curl Request

### Request
```bash
curl -X POST \
http://localhost:8080/jobs/metrics/signal \
-H 'Content-Type: application/json' \
-d '{
"parameters": {
"data_source": "my_data_source",
"signal": "my_signal"
}
}'
```

### Curl Response
```bash
{
"id": "123e4567-e89b-12d3-a456-426655440000",
"kind": "signal_metrics",
"created_at": "2023-05-18T10:10:10.000Z",
"status": "pending",
"error_message": null,
"traceback": null,
"result": null,
"parameters": {
"data_source": "my_data_source",
"signal": "my_signal"
},
"current_progress": null
}
```

## Go server

### Struct
```go
type CreateSignalMetricsJobRequest struct {
Kind JobKind `json:"kind"`
Parameters SignalMetricsParametersRequest `json:"parameters"`
}
```

### Handler
```go
func (h *jobHandler) CreateSignalMetricsJob(w http.ResponseWriter, r *http.Request) {
var req CreateSignalMetricsJobRequest
body, err := ioutil.ReadAll(r.Body)
if err != nil {
h.l.Println(err)
w.WriteHeader(http.StatusInternalServerError)
fmt.Fprintln(w, err)
return
}
r.Body = ioutil.NopCloser(bytes.NewBuffer(body))
err = json.Unmarshal(body, &req)
if err != nil {
h.l.Printf("Failed to unmarshal request: %s", err)
w.WriteHeader(http.StatusBadRequest)
fmt.Fprintln(w, "Failed to unmarshal request")
return
}

job, err := h.jobService.CreateSignalMetricsJob(req)
if err != nil {
h.l.Printf("Failed to create job: %s", err)
w.WriteHeader(http.StatusInternalServerError)
fmt.Fprintln(w, "Failed to create job")
return
}

w.WriteHeader(http.StatusCreated)
w.Header().Set("Content-Type", "application/json")
enc := json.NewEncoder(w)
err = enc.Encode(job)
if err != nil {
h.l.Printf("Failed to encode response: %s", err)
w.WriteHeader(http.StatusInternalServerError)
fmt.Fprintln(w, "Failed to encode response")
return
}
}
```
## Links

- [Jobs.create_signal_metrics_job](https://github.com/octopize/avatar-python/blob/0.6.2/avatars/api.py#L583)
- [SignalMetricsJobCreate](https://github.com/octopize/avatar-python/blob/0.6.2/avatars/api.py#L583)
- [SignalMetricsJob](https://github.com/octopize/avatar-python/blob/0.6.2/avatars/api.py#L583)

## Automated Issue Details

Dear visitor,

This issue has been automatically generated from the Octopize project [avatar-python](https://github.com/octopize/avatar-python/) to make SIGO compatible. Please vote with a thumbs up or thumbs down to assess the quality of the automatic generation.

Best regards,
The SIGO Team

Start with the CreateSignalMetricsJob handler and the linked Jobs.create_signal_metrics_job, SignalMetricsJobCreate, and SignalMetricsJob references. Trace how the Go server creates other jobs, then verify that POST /jobs/metrics/signal accepts the documented parameters and returns the specified pending job response.

Written by the indexing model from the issue text.