Cache Icons

[epheterson]

I noticed you had us create an icons directory with the docker run command:

docker run  \
  --name homarr \
  --restart unless-stopped \
  -p 7575:7575 \
  -v ./homarr/configs:/app/data/configs \
  -v ./homarr/icons:/app/public/icons \
  -d ghcr.io/ajnart/homarr:latest

I figured this would be used with icons automatically grabbed from the HomeLab icon set (great feature, by the way!). Just in case the icon site is ever down, and to reduce the number of trips to the internet (and load on their servers), it'd be nice if Homarr cached the icon instead of always reaching out to download it.