Hi @Francis Rohner ,
Please check if the suggestions from below link could help you. Using VS Add-in Wizard to create your addin project.
https://www.codeproject.com/Articles/1073839/Create-SQL-Server-Management-Studio-Addin
https://stackoverflow.com/questions/47366483/vsix-extension-for-ssms-context-menu-for-result-grid
If the response is helpful, please click "Accept Answer" and upvote it, thank you.