Feature: #106477 - Allow YAML imports and placeholder processing when creating new forms 

Description 

The FormManagerController now uses the YamlFileLoader when creating new forms from templates. This change enables the processing of placeholders within template files, such as environment variables in the format %env(ENV_NAME)%, as well as the import of other YAML files.

This enhancement allows for more flexible form templates that can adapt to different environments through environment variable substitution and YAML imports.

Examples 

imports:
  - { resource: 'User.yaml' }
identifier: contactForm
label: 'Contact Form %env(ENV_NAME)%'
type: Form
renderables:
  -
    type: Page
    identifier: message
    label: Message
    renderables:
      -
        defaultValue: ''
        type: Text
        identifier: text-1
        label: Subject

renderables:
  -
    type: Page
    identifier: user
    label: User data
    renderables:
      -
        defaultValue: ''
        type: Text
        identifier: username
        label: Username

Impact 

Form templates can now contain environment variable placeholders using the %env(ENV_NAME)% syntax and import other YAML files. These placeholders and imports are automatically resolved when new forms are created from the template.