Interpolate object parameters as JSON strings

When trating object parameters as `map`s, the interpolation of the
object itself changes to the string representation of `map` instead of
the previous JSON string representation.

In order to keep the old behaviour of interpolating the object parameter
to a JSON string, this change introduces a new type, `FormattedObject`,
which implements the [`fmt.Formatter`](https://pkg.go.dev/fmt#Formatter)
interface. The implemented `Format` function turns the object's string
representation into a JSON string, instad of the default Go
representation of a `map`.

Example:

```yaml
parameter:
  - name: foo
    type: object
    default:
      bar: 1

install:
  mymixin:
    # Interpolating a nested property of the object parameter.
    val: "${ bundle.parameter.foo.bar }" # -> `val: '1'`

    # Interpolating the object parameter directly.
    obj: "${ bundle.parameter.foo }"     # -> `obj: '{"bar":1}'`
```

A shortcoming of this implementation is that interpolating nested
properties which also are `map` types will result in the interpolated
value being the string representation of `map`.

pkg/runtime/runtime_manifest.go

@@ -132,6 +132,19 @@ func (m *RuntimeManifest) loadDependencyDefinitions() error {
 	return nil
 }
 
+// This wrapper type serve as a way of formatting a `map[string]interface{}` as
+// JSON when the templating by mustache is done. It makes it possible to
+// maintain the JSON string representation of the map while still allowing the
+// map to be used as a context in the templating, allowing for accessing the
+// map's keys in the template.
+type FormattedObject map[string]interface{}
+
+// Format the `FormattedObject` as a JSON string.
+func (fo FormattedObject) Format(f fmt.State, c rune) {
+	jsonStr, _ := json.Marshal(fo)
+	fmt.Fprintf(f, string(jsonStr))
+}
+
 func (m *RuntimeManifest) resolveParameter(pd manifest.ParameterDefinition) (interface{}, error) {
 	getValue := func(envVar string) (interface{}, error) {
 		value := m.config.Getenv(envVar)
@@ -140,7 +153,7 @@ func (m *RuntimeManifest) resolveParameter(pd manifest.ParameterDefinition) (int
 			if err := json.Unmarshal([]byte(value), &obj); err != nil {
 				return nil, err
 			}
-			return obj, nil
+			return FormattedObject(obj), nil
 		}
 		return value, nil
 	}

pkg/runtime/runtime_manifest_test.go

@@ -48,7 +48,8 @@ install:
 - mymixin:
     Parameters:
       Thing: ${ bundle.parameters.person }
-      Object: ${ bundle.parameters.contact.name }
+      ObjectName: ${ bundle.parameters.contact.name }
+      Object: '${ bundle.parameters.contact }'
 `
 	rm := runtimeManifestFromStepYaml(t, testConfig, mContent)
 	s := rm.Install[0]
@@ -66,13 +67,19 @@ install:
 	assert.Equal(t, "Ralpha", val)
 	assert.NotContains(t, "place", pms, "parameters that don't apply to the current action should not be resolved")
 
-	// New assertions for the contact parameter
-	require.IsType(t, "string", pms["Object"], "Data.mymixin.Parameters.Object has incorrect type")
-	contactName := pms["Object"].(string)
-	require.IsType(t, "string", contactName, "Data.mymixin.Parameters.Object.name has incorrect type")
-
+	// Asserting `bundle.parameters.contact.name` works.
+	require.IsType(t, "string", pms["ObjectName"], "Data.mymixin.Parameters.ObjectName has incorrect type")
+	contactName := pms["ObjectName"].(string)
+	require.IsType(t, "string", contactName, "Data.mymixin.Parameters.ObjectName.name has incorrect type")
 	assert.Equal(t, "Breta", contactName)
 
+	// Asserting `bundle.parameters.contact` evaluates to the JSON string
+	// representation of the object.
+	require.IsType(t, "string", pms["Object"], "Data.mymixin.Parameters.Object has incorrect type")
+	contact := pms["Object"].(string)
+	require.IsType(t, "string", contact, "Data.mymixin.Parameters.Object has incorrect type")
+	assert.Equal(t, "{\"name\":\"Breta\"}", contact)
+
 	err = rm.Initialize(ctx)
 	require.NoError(t, err)
 }