Allow a setting in a unit's name only as a template's whole instance, never leading with a dash, at most 64 characters

Third review of mesh-catalog #147. A setting anywhere else in a unit's name could make the unit another
unit or another kind; it is now refused where the manifest is read. A value beginning with '-' would be
read by systemctl as an option, and a long one is no pool's name.

internal/catalogue/manifest.go

@@ -1759,6 +1759,7 @@ func ParseManifest(raw []byte) (Manifest, error) {
 	}
 	problems = append(problems, invokeProblems(m)...)
 	problems = append(problems, replacesProblems(m)...)
+	problems = append(problems, UnitSettingProblems(m)...)
 	problems = append(problems, endpointNameProblems(m)...)
 	problems = append(problems, RouteProblems(m)...)
 	for _, port := range m.Guards {