Add "coding" as a Marketplace category

[mrsimonemms]

This issue is a:

• [ ] Bug Report
• [x] Enhancement suggestion
• [ ] Feature request

Enhancement suggestions / feature requests

It would be nice to have a coding category in the manifest.yaml for Marketplace applications. I'm currently developing a Gitpod Marketplace app. There are also other remote coding applications that could make use of this category.

NB. I've made the suggestion as coding - I'm not against it being any other synonym such as development, ide or anything else you can think of