feat(kubeshell) allow overriding default kubeshell image EE-1756 (#5755)

* feat(kubeshell) allow overriding default kubeshell

* Add missing error check and struct tag

* Add migrator for kube shell image and add it as a default in the db

* Fix file name to match migrator pattern

* remove default as it's now coming from the db

* remove blank line

* - conflict resolution code update
- logging migration error on migration failures

* - migrateDBVersionTo34 -> migrateDBVersionToDB34 (naming consistency)

Co-authored-by: zees-dev <dev.786zshan@gmail.com>

api/http/handler/settings/settings_update.go

@@ -40,6 +40,8 @@ type settingsUpdatePayload struct {
 	EnableTelemetry *bool `example:"false"`
 	// Helm repository URL
 	HelmRepositoryURL *string `example:"https://charts.bitnami.com/bitnami"`
+	// Kubectl Shell Image
+	KubectlShellImage *string `example:"portainer/kubectl-shell:latest"`
 }
 
 func (payload *settingsUpdatePayload) Validate(r *http.Request) error {
@@ -178,6 +180,10 @@ func (handler *Handler) settingsUpdate(w http.ResponseWriter, r *http.Request) *
 		return tlsError
 	}
 
+	if payload.KubectlShellImage != nil {
+		settings.KubectlShellImage = *payload.KubectlShellImage
+	}
+
 	err = handler.DataStore.Settings().UpdateSettings(settings)
 	if err != nil {
 		return &httperror.HandlerError{http.StatusInternalServerError, "Unable to persist settings changes inside the database", err}