added celebration banner

[nheek]

• Added a celebration banner based on the existing button component so it's consistent with the already existing design
• Added fireworks
• Used the text on the Instagram post where the links point to the same links but changed the names to their non-Instagram-username counterparts
• Added custom_hero to config.toml so we don't need to rename it in the future but haven't deleted the old bosko one yet in case
• Also changed the corresponding part in index to custom_hero instead of the bosko one
• Added .DS_Store to .gitignore since I'm using a Mac

[nheek]

@timharek thank you for pointing these out! I've now fixed them. I haven't added any article though because I don't think I'm the best person to write this. At least not in Norwegian.

[nheek]

Oi! Har nettopp merkert meg at du faktisk hadde skrevet norsk til meg og ikke engelsk. Beklager!