worker: define job types as constants

Define supported job type names as constants and use them in all places,
instead of string literals.

There are multiple benefits of this approach. Using constants removed
the room for typos in the string literals. One can use autocompletion in
IDE for job types. Using constant makes it easier to find all references
where it is used and thus all places that are handling a specific job
type.

cmd/osbuild-worker/main.go

@@ -170,7 +170,7 @@ func RequestAndRunJob(client *worker.Client, acceptedJobTypes []string, jobImpls
 
 	// Depsolve requests needs reactivity, since setting the protection can take up to 6s to timeout if the worker isn't
 	// in an AWS env, disable this setting for them.
-	if job.Type() != "depsolve" {
+	if job.Type() != worker.JobTypeDepsolve {
 		setProtection(true)
 		defer setProtection(false)
 	}
@@ -420,7 +420,7 @@ func main() {
 	defer depsolveCtxCancel()
 	go func() {
 		jobImpls := map[string]JobImplementation{
-			"depsolve": &DepsolveJobImpl{
+			worker.JobTypeDepsolve: &DepsolveJobImpl{
 				Solver: solver,
 			},
 		}
@@ -448,7 +448,7 @@ func main() {
 
 	// non-depsolve job
 	jobImpls := map[string]JobImplementation{
-		"osbuild": &OSBuildJobImpl{
+		worker.JobTypeOSBuild: &OSBuildJobImpl{
 			Store:                  store,
 			Output:                 output,
 			KojiServers:            kojiServers,
@@ -466,17 +466,17 @@ func main() {
 				SkipSSLVerification: genericS3SkipSSLVerification,
 			},
 		},
-		"osbuild-koji": &OSBuildKojiJobImpl{
+		worker.JobTypeOSBuildKoji: &OSBuildKojiJobImpl{
 			Store:              store,
 			Output:             output,
 			KojiServers:        kojiServers,
 			relaxTimeoutFactor: config.RelaxTimeoutFactor,
 		},
-		"koji-init": &KojiInitJobImpl{
+		worker.JobTypeKojiInit: &KojiInitJobImpl{
 			KojiServers:        kojiServers,
 			relaxTimeoutFactor: config.RelaxTimeoutFactor,
 		},
-		"koji-finalize": &KojiFinalizeJobImpl{
+		worker.JobTypeKojiFinalize: &KojiFinalizeJobImpl{
 			KojiServers:        kojiServers,
 			relaxTimeoutFactor: config.RelaxTimeoutFactor,
 		},