✨ feat(main.go): add index.html route to display available routes and…

… url params

🐛 fix(main.go): fix picsum route to return the same content type as the request
✨ feat(main.go): add checkError function to handle errors and return http status codes
✨ feat(main.go): add stringToInt64 function to convert string to int64 for seed
✨ feat(main.go): add getWHUrlParams function to get width and height url params and check if they are in range
✨ feat(main.go): add seed to picsum route and print it to console
✨ feat(main.go): add support for configurable port from .env file in main function and print it to console

gitignore added

... something called merge ...