worker/koji-finalize: handle multiple upload targets

Enhance the `koji-finalize` job implementation to be able to cope with
multiple upload targets being specified for an `OSBuildJob`.

Implement a convenience method `OSBuildJobResult.TargetResultsByName()`
for filtering the target results attached to the job result by their
name. Cover the method with an unit test. And lastly use this method in
the `koji-finalize` job to find the appropriate Koji upload target
results.

This is a preparation for enabling cloud uploads for Koji composes.

internal/worker/json.go

@@ -75,6 +75,20 @@ func (j *OSBuildJobResult) TargetErrors() []*clienterrors.Error {
 	return targetErrors
 }
 
+// TargetResultsByName iterates over TargetResults attached to the Job result and
+// returns a slice of Target results of the provided name (type). If there were no
+// TargetResults of the desired type attached to the Job results, the returned
+// slice will be empty.
+func (j *OSBuildJobResult) TargetResultsByName(name target.TargetName) []*target.TargetResult {
+	targetResults := []*target.TargetResult{}
+	for _, targetResult := range j.TargetResults {
+		if targetResult.Name == name {
+			targetResults = append(targetResults, targetResult)
+		}
+	}
+	return targetResults
+}
+
 type KojiInitJob struct {
 	Server  string `json:"server"`
 	Name    string `json:"name"`