Add support to esm blueprints.

[mshima]

Node community is adopting esm and commonjs packages cannot depend on esm packages.
By allowing blueprints to switch to esm, will make easier esm adoption on generator-jhipster probably for v8.

Why this is needed?
require() doesn't exist on an esm module. It was replaced by the async import().
So every operation that depend on dynamically loading a module (like a blueprint), need to be converted to async.
A constructor is always sync, as workaround, an async _postConstruct needs to be used to wait for the blueprint to be instantiated.

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