add AnsiEsc to install_vim

[jinal--shah]

Useful for viewing colourised log output e.g. anything from hashicorp cli tools

Would be something like:

# TODO some kind of additional loop for when we don't get the vimball, but a sourceforge error page
curl -sS -L --retry 3 \
  -o /var/tmp/AnsiEsc.vba.gz "https://vim.sourceforge.io/scripts/download_script.php?src_id=14498" 

gunzip /var/tmp/AnsiEsc.vba.gz
mkdir /etc/vim/bundle/AnsiEsc
su-exec root vim -c 'e /var/tmp/AnsiEsc.vba' -c 'UseVimball /etc/vim/bundle/AnsiEsc' -c 'q'

# modify AnsiEsc to restore our own custom settings properly:
sed -i '/let &l:hl= s:hlkeep_{bufnr("%")}/a so $MYVIMRC' /var/tmp/AnsiEsc.vim | grep -B3 MYVIMRC