[Boot] Automatic configuration of repositories in Application

[kjdelisle]

blocked by #780

Story

As a LoopBack 4 user, I would like all of the repository files I place (or generate!) in ./src/repositories to automatically be associated with my Application so that I don't have to type app.repository(...) over and over again.

Acceptance Criteria

• If the Application is not using the RepositoryMixin, ignore the contents of /src/repositories.
• Must read all files of the format *.repository.js from the repositories directory
• Must associate all of the repository exported classes with the application using the .repository function.
• Take each exported class from the *.repository.js file (subject to change based on user feedback)
• [ ] There should be a blog post informing users that this is now live (once this change has been released!), and explain how it works.
• Docs on loopback.io
• Refactor/update example code (loopback4-example-getting-started)
• Check that app template(s) in CLI already use @loopback/boot (and if not, fix this)

[dhmlau]

FYI - please check with @raymondfeng when picking up this task. Some of the ideas in boot for LB3 can be reused.

[virkt25]

As per a discussion with @kjdelisle, the blog for @loopback/boot will cover the Repository Booter since this alone doesn't provide enough content for a blog post.

PRs landed. Closing this.