[NEOS-683] Job Run metadata always assuming one type of metadata

[nickzelei]

this results in an empty metadata object.

we should be looser here about the metadata we parse as it will be different per activity.

right now the backend always assumes a specific shape and returns it as such.

			if len(attributes.Input.Payloads) > 1 {
				var input mgmtv1alpha1.JobRunSyncMetadata
				err := converter.GetDefaultDataConverter().FromPayload(attributes.Input.Payloads[1], &input)
				if err != nil {
					logger.Error(fmt.Errorf("unable to convert event input payload: %w", err).Error())
				}
				jobRunEvent.Metadata = &mgmtv1alpha1.JobRunEventMetadata{
					Metadata: &mgmtv1alpha1.JobRunEventMetadata_SyncMetadata{
						SyncMetadata: &mgmtv1alpha1.JobRunSyncMetadata{
							Schema: input.Schema,
							Table:  input.Table,
						},
					},
				}
			}

_{From SyncLinear.com | NEOS-683}