Is your feature request related to a problem? Please describe.
Maintaining OS specific "manifest" (darwin/Info.plist, windows/<project>.exe.manifest, windows/info.json) is a bit tedious, especially because they contain a lot of duplication. And updating them is error prone.

Describe the solution you'd like
Having a single source of truth, such as wails.json, that will be used to populate the content of these manifests.

This will require the ProjectData to be used to generate a default configuration for each OS. If a manifest already exists, and that the common properties are defined then the manifest values takes precedence. Basically, a merge.

So, during packaging:

1. No manifest -> auto-generation from wails.json
2. Existing manifest -> merge with priority to the manifest values.

Describe alternatives you've considered
None.

Additional context
N/A

Of course, if I can help getting this done... :)