Import of main chunk from bootstrap should be lazily evaluated

**Enhancement**
At the moment the main.js chunk is imported lazily from the bootstrap entry but is executed immediately. If we want to preload this up front in the future we need to make this lazily executed.

Start by locating the bootstrap entry and the lazy import of the main.js chunk. Trace when that import executes, then use the existing tests or build checks to verify that preloading the chunk does not execute it until it is explicitly requested.

Written by the indexing model from the issue text.