Code review comment for ~xnox/launchpad:copy-signing-bool

My biggest concern here is that the selection of custom upload types to exclude seems quite arbitrary just from looking at the code here, and it's not going to be obvious to future developers what overall properties of the system they need to maintain. At the moment I'm not even sure I understand the rationale well enough to be clear on whether this is the best approach.

Could you please add some commentary somewhere (in the actual code, not just in supporting material such as commit messages or merge proposal conversations) that explains the "why" of this change, as well as the "what"?