add new 'KeepLast state for 'NoData' and 'ExecErrState' on alert rule…

[Gedulis12]

Added 'KeepLast' to *NoDataStatePropEnum and *ExecErrStatePropEnum on grafana alert rule models. This fixes a bug where if 'Keep Last State' is selected as no data error handling, go client api alert validation fails with error:

noDataState in body should be one of [Alerting NoData OK]

See example code snippet:

func getAlertRules(api *goapi.GrafanaHTTPAPI) (models.ProvisionedAlertRules, error) {
	svc := api.Provisioning
	resp, err := svc.GetAlertRules()
	if err != nil {
		return nil, err
	}
	for _, r := range resp.Payload {
		err = r.Validate(strfmt.Default)
		if err != nil {
			fmt.Println("----------")
			fmt.Println("Validation failed for alert: ", *r.Title, " UID: ", r.UID)
			fmt.Println(*r.NoDataState)
			fmt.Println(err)
		}
	}
	return resp.Payload, nil
}

And stdout:

----------
Validation failed for alert:  <Redacted Title>  UID:  <Redacted Uid>
KeepLast
validation failure list:
noDataState in body should be one of [Alerting NoData OK]

[CLAassistant]

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Due to failing check

[Gedulis12]

@nikimanoledaki i realised i'm not supposed to edit the code directly as it's being generated from the openapispec, i have updated the script pulling and modifying the spec file, can we try running the validation tests again?