Allow users to make custom changes to manifests before submission

Description of the new feature/enhancement

After the initial set of prompts, wingetcreate shows a summary and then asks whether the user wants to make any changes to the generated manifest. If confirming with yes, the tool goes through the same set of prompts again without giving the user an option to manually make custom changes. If users want to add additional manifest fields, they have to open and edit the manifest files manually in a text editor, save, then go back to wingetcreate to submit a PR.

I suggest to make it easier for users to customize the manifest before submitting it. One option could be to allow registering a text editor with wingetcreate (e.g. VS Code). wingetcreate could then ask if the user wants to make custom changes to the manifest, and if yes, open the text editor with the three manifest files, wait until the user has made changes and closed the editor, then continue with the submission.

This kind of workflow is not really new, e.g. git uses this mechanism for many of its features (e.g. commit message editing, interactive rebase).

Start by tracing wingetcreate's prompt, manifest-generation, and submission flow described in the issue. Determine how the generated manifest files can be opened in a user-selected editor and how the tool should detect completion; done means users can make custom changes to all three manifests before submission continues.