Initializer of repository content. A component that needs to add specific
content to a new repository can implement this interface. Then when a
repository becomes available, all the configured initializers are invoked
Initializes repository content. This method is called as soon as a
repository becomes available. Note that the repository may already
have been initialized, so the implementation of this method should
check for that before blindly adding new content.
builder - builder for accessing and modifying repository content