Add option to configure template job HCL file

Previously, the template job HCL file was hardcoded using go:embed
in the binary. However, this did not allow users running Poseidon
to change its content. Now, users can change the content of the
template job HCL file using the configuration option.

internal/environment/manager.go

@@ -10,6 +10,7 @@ import (
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/internal/runner"
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/pkg/dto"
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/pkg/logging"
+	"os"
 	"strconv"
 )
 
@@ -39,13 +40,35 @@ type Manager interface {
 func NewNomadEnvironmentManager(
 	runnerManager runner.Manager,
 	apiClient nomad.ExecutorAPI,
-) *NomadEnvironmentManager {
-	m := &NomadEnvironmentManager{runnerManager, apiClient, *parseJob(templateEnvironmentJobHCL)}
+	templateJobFile string,
+) (*NomadEnvironmentManager, error) {
+	if err := loadTemplateEnvironmentJobHCL(templateJobFile); err != nil {
+		return nil, err
+	}
+	templateEnvironmentJob, err := parseJob(templateEnvironmentJobHCL)
+	if err != nil {
+		return nil, err
+	}
+	m := &NomadEnvironmentManager{runnerManager, apiClient, *templateEnvironmentJob}
 	if err := m.Load(); err != nil {
 		log.WithError(err).Error("Error recovering the execution environments")
 	}
 	runnerManager.Load()
-	return m
+	return m, nil
+}
+
+// loadTemplateEnvironmentJobHCL loads the template environment job HCL from the given path.
+// If the path is empty, the embedded default file is used.
+func loadTemplateEnvironmentJobHCL(path string) error {
+	if path == "" {
+		return nil
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return fmt.Errorf("error loading template environment job: %w", err)
+	}
+	templateEnvironmentJobHCL = string(data)
+	return nil
 }
 
 type NomadEnvironmentManager struct {
@@ -116,7 +139,7 @@ func (m *NomadEnvironmentManager) Load() error {
 	return nil
 }
 
-func parseJob(jobHCL string) *nomadApi.Job {
+func parseJob(jobHCL string) (*nomadApi.Job, error) {
 	config := jobspec2.ParseConfig{
 		Body:    []byte(jobHCL),
 		AllowFS: false,
@@ -124,9 +147,8 @@ func parseJob(jobHCL string) *nomadApi.Job {
 	}
 	job, err := jobspec2.ParseWithConfig(&config)
 	if err != nil {
-		log.WithError(err).Fatal("Error parsing Nomad job")
-		return nil
+		return nil, fmt.Errorf("error parsing Nomad job: %w", err)
 	}
 
-	return job
+	return job, nil
 }