Docs: Add support for Monorepo project docs generation

[maschad]

Following up on the conversation here we should work out a way to handle generating docs for monorepos.

TypeDoc's entryPointStrategy: packages is dedicated support for monorepo projects, it will attempt to determine entry points based on package.json's main property (with default value index.js) and if it wasn't found, based on types property.

For most for aegir-managed projects monorepos seem to have the projects listed under the packages directory, we could default to this and use the packages entryPointStrategy and pass the paths.

Otherwise we could have an optional monoRepoEntryPoints flag that a user could pass as an argument and then we pass that to the entryPointStrategy argument.