Add custom.css and custom.js to the ConfigMap [Feature]

[brianramseyau]

Firstly, thank you for the chart, very helpful to get up and running quickly.

Would be great to be able to pass in arbitrary css/js through the chart also, per the directions here: https://gethomepage.dev/v0.9.1/configs/custom-css-js/

Should just be adding to the ConfigMap but would need to be slightly different to the others in that it wouldn't be YAML.