[Feature Request] Create `.png` image from `.greenshot` file via CLI

Hello,

I would like to see Greenshot to run via CLI too.

Imagine my situation why I would like to get this option:

I write wiki pages via MkDocs which supports Markdown language and to edit `.md` files I use VS Code. I can put `.png` images by file path into Markdown.

When I capture a region with Greenshot I want to save it as original source file (`.greenshot` file format) so I can later edit the image if desired. This is already possible.

Now I want to convert the original source file to `.png` file for example. It's possible to do it manually via Greenshot Editor - Save As but I would like to automate this process via CLI. For example:

`greenshot convert --source 20220104-104422.greenshot --format png`

or something like that and it will simply create a new `.png` file in the same folder as the source file and the source file will stay untouched.

Then I can automate this process in VS Code with a watch task and Gulp to run such a command when `.greenshot` file is changed so it will automatically regenerate `.png` file.

Of course, you should add support for other image file formats too...

Thanks.