feat: Create and secure a secrets directory as part of stacks install

Even though Nginx Proxy Manager currently uses the `secrets` directory, it makes sense to
create this directory as part of the general stacks installer. Furthermore, it should be
secured by the installer so that this secure step doesn't have to be manually accomplished
later.

Backup processes that use rsync to pull down files from servers may encounter problems,
though, if the user doesn't have access to the files, even if they are using rsync with
sudo. So, we offer to set the `secrets` directory to a group that the real user has access
to. It's just more natural, convenient, and functional.

stacks/setup.sh

@@ -2,6 +2,44 @@
 
 scr_dir="${0%/*}"
 
+# Collect user groups. We do this in the background right away since a server connected to AD may take
+# several seconds to respond with the group list.
+real_user=${SUDO_USER:-$(whoami)}
+groups_file=$(mktemp)
+(id "$real_user" | cut -d'=' -f4 | tr ',' '\n' > "$groups_file") &
+groups_pid="$!"
+
+# Create secrets directory
+sec_dir=$(realpath "$scr_dir/..")/secrets
+mkdir -p "$sec_dir"
+
+# Set strict permissions for the secrets
+echo "It is highly recommended that you restrict permissions of the $(tput smul)$(basename "$sec_dir")$(tput rmul) directory."
+echo "I can set the group to something your $real_user user also has access to."
+read -r -p "Do you want to do this? [Y/n] " yorn
+if [[ ${yorn:-y} =~ [Yy] ]]; then
+   echo -n "Great! Finding your user groups."
+   while ps "$groups_pid" > /dev/null; do echo -n '.'; sleep 1; done
+   echo -e '\n'
+   while IFS=$'\n' read -r line; do
+      group_array+=("$line")
+   done <<< "$(<"$groups_file")"
+   PS3="Either enter a number or manually type a group name: "
+   select group in "${group_array[@]}"; do
+      # Accept either the selected group or the manually-entered group
+      group=${group:-$REPLY}
+      # Don't accept a blank entry
+      [[ -n $group ]] && break
+   done
+   echo "Setting the group of the $(tput smul)$(basename "$sec_dir")$(tput rmul) directory to $(tput smul)$group$(tput rmul)."
+   # Groups will look like "123(group_name)", so we get just the number by looking to the left of '('.
+   # This will also work with manually entered groups like "group_name" or "123".
+   group=$(echo "$group" | cut -d'(' -f1)
+   chgrp -R "$group" "$sec_dir"
+   chmod -R 770 "$sec_dir"
+fi
+
+# Install individual stacks
 for stackinstaller in "$scr_dir"/*-install.sh; do
    stackname="$(basename "$stackinstaller" | sed -e "s/-install.sh//")"
    echo -n "Do you want to install $stackname? [Y/n]: "