Use asset manifest to read bundle sizes

[Ferrus91]

Description

A request to add a config option to read and use asset manifest file instead of a file glob pattern.

Motivation and Context

With react create apps and other such programs it can be difficult to know before hand what your file structure is, and in any case webpack can change it requiring the globs to change.

This is a simple solution to allow a config option to read a assets-manifest, so that it then goes and reads through that manifest and performs bundle size calculattions on them all

This is related to this open issue: #309

Screenshots (if appropriate):

Types of changes

• New feature (non-breaking change which adds functionality)