Better error message in case of conversion error (#3402)

## Changes
Improve error message when converting typed struct to dynamic.

## Why
Currently different functions share the message body, so you don't know
which field failed to convert.

Real example when working on #3390
test acceptance/bundle/deploy/jobs/double-underscore-keys triggers this
error condition:

Before this change "bundle deploy" fails with:

```
Warn: unable to convert typed configuration to dynamic configuration: unhandled type: string
Error: exit error: unhandled type: string
```

After:

```
Warn: unable to convert typed configuration to dynamic configuration: cannot convert int field to dynamic type "string": src=4611686018427387911 ref="4611686018427387911"
Error: exit error: cannot convert int field to dynamic type "string": src=4611686018427387911 ref="4611686018427387911"
```

## Tests
Manually, by applying this commit on
#3390

Author: denik

libs/dyn/convert/from_typed.go

@@ -96,7 +96,7 @@ func fromTypedStruct(src reflect.Value, ref dyn.Value, options ...fromTypedOptio
 		}
 	case dyn.KindMap, dyn.KindNil:
 	default:
-		return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+		return dyn.InvalidValue, fmt.Errorf("cannot convert struct field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 	}
 
 	refm, _ := ref.AsMap()
@@ -161,7 +161,7 @@ func fromTypedMap(src reflect.Value, ref dyn.Value) (dyn.Value, error) {
 		}
 	case dyn.KindMap, dyn.KindNil:
 	default:
-		return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+		return dyn.InvalidValue, fmt.Errorf("cannot convert map field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 	}
 
 	// Return nil if the map is nil.
@@ -209,7 +209,7 @@ func fromTypedSlice(src reflect.Value, ref dyn.Value) (dyn.Value, error) {
 		}
 	case dyn.KindSequence, dyn.KindNil:
 	default:
-		return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+		return dyn.InvalidValue, fmt.Errorf("cannot convert slice field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 	}
 
 	// Return nil if the slice is nil.
@@ -257,7 +257,7 @@ func fromTypedString(src reflect.Value, ref dyn.Value, options ...fromTypedOptio
 		return dyn.V(src.String()), nil
 	}
 
-	return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+	return dyn.InvalidValue, fmt.Errorf("cannot convert string field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 }
 
 func fromTypedBool(src reflect.Value, ref dyn.Value, options ...fromTypedOptions) (dyn.Value, error) {
@@ -282,7 +282,7 @@ func fromTypedBool(src reflect.Value, ref dyn.Value, options ...fromTypedOptions
 		}
 	}
 
-	return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+	return dyn.InvalidValue, fmt.Errorf("cannot convert bool field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 }
 
 func fromTypedInt(src reflect.Value, ref dyn.Value, options ...fromTypedOptions) (dyn.Value, error) {
@@ -307,7 +307,7 @@ func fromTypedInt(src reflect.Value, ref dyn.Value, options ...fromTypedOptions)
 		}
 	}
 
-	return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+	return dyn.InvalidValue, fmt.Errorf("cannot convert int field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 }
 
 func fromTypedFloat(src reflect.Value, ref dyn.Value, options ...fromTypedOptions) (dyn.Value, error) {
@@ -332,7 +332,7 @@ func fromTypedFloat(src reflect.Value, ref dyn.Value, options ...fromTypedOption
 		}
 	}
 
-	return dyn.InvalidValue, fmt.Errorf("unhandled type: %s", ref.Kind())
+	return dyn.InvalidValue, fmt.Errorf("cannot convert float field to dynamic type %#v: src=%#v ref=%#v", ref.Kind().String(), src, ref.AsAny())
 }
 
 func getForceSendFields(v reflect.Value) []string {