Update application generator to register targetDefaults

[tbinna]

Update the application generator to register targetDefaults. This should help to remove target definitions where the targets are configured with the default values.

Refer to the targetDefaults reference docs for details on how to define target defaults. For example, we can use placeholder tokens such as {workspaceRoot} and {projectRoot} to define outputs.

Refer to the node application generator for an example of how to do this: https://github.com/nrwl/nx/blob/6485e3cc4adcd646628693d65d9053d076b7575a/packages/node/src/generators/application/application.ts#L169