Add PCB backplate template for generic 83x58x33mm enclosure

PCB Backplane template for generic 83x58x33mm waterproof enclosure. Unbranded but very common and easily available in online markets with search term: "83x58x33mm enclosure".

They came in multiple options: gray cover, clear cover, with wall mounting tabs, etc. All of them have the same layout inside .

Some vendor mark is KH-F19, but there are a lot of them without markings. For example AK10019-A1 and its respective drawing here