clean up old docker desktop broken symlink before rancher install (#86)

@chadgh and @ark134 both hit this "Permission denied" issue while they
were reinstalling rancher:
```
==> Moving App 'Rancher Desktop.app' to '/Applications/Rancher Desktop.app'
:beer:  ih-rancher was successfully installed!
==> `brew cleanup` has not been run in the last 30 days, running now...
Disable this behaviour by setting HOMEBREW_NO_INSTALL_CLEANUP.
Hide these hints with HOMEBREW_NO_ENV_HINTS (see `man brew`).
Error: Permission denied @ apply2files - /usr/local/lib/docker/cli-plugins
WARN: Could not install Rancher Desktop
```

Seems like the best way to handle this is by deleting the broken
symlink: https://stackoverflow.com/a/75141533

Here's what I see locally, which confirms docker leaves this broken
after uninstalling:
```
$ ls -hal /usr/local/lib/docker/cli-plugins
lrwxr-xr-x  1 root  wheel    55B Jan 25  2022 /usr/local/lib/docker/cli-plugins -> /Applications/Docker.app/Contents/Resources/cli-plugins
$ ls -hal /Applications/Docker.app/Contents/Resources/cli-plugins
ls: /Applications/Docker.app/Contents/Resources/cli-plugins: No such file or directory
```

This PR adds some additional clean-up logic to the clean up the broken
symlink before proceeding with the rancher install.

VERSION

@@ -1 +1 @@
-0.1.47
+0.1.48

formula/ih-core.rb

@@ -1,5 +1,5 @@
 class IhCore < Formula
-  VERSION="0.1.47"
+  VERSION="0.1.48"
   desc "Brew formula for installing core tools used at Included Health engineering."
   homepage "https://github.com/ConsultingMD/homebrew-ih-public"
   license "CC BY-NC-ND 4.0"

lib/core/rancher/step.sh

@@ -70,12 +70,25 @@ function ih::setup::core.rancher::deps() {
 }
 
 function ih::setup::core.rancher::install() {
-  local THIS_DIR="$IH_CORE_LIB_DIR/core/rancher"
+  # Clean up old docker symlink to prevent "Permission denied" error
+  # More details: https://stackoverflow.com/a/75141533
+  local SYMLINK_PATH="/usr/local/lib/docker/cli-plugins"
+  if [ -L "$SYMLINK_PATH" ]; then
+    local TARGET_PATH=$(readlink "$SYMLINK_PATH")
+    if [ ! -d "$TARGET_PATH" ]; then
+      sudo rm -f "$SYMLINK_PATH"
+      ih::log::info "Removed broken symlink from old docker install at $SYMLINK_PATH"
+
+      brew cleanup
+      ih::log::info "Homebrew cleanup completed."
+    fi
+  fi
 
   cp -f "$RANCHER_AUGMENT_SRC" "$RANCHER_AUGMENT_DST"
 
   echo "A configuration file for Rancher Desktop will be copied to your system"
   echo "You may be required to enter your password"
+  local THIS_DIR="$IH_CORE_LIB_DIR/core/rancher"
   sudo cp "${THIS_DIR}/io.rancherdesktop.profile.defaults.plist" "$PLIST_DST"
 
   # Check if Rancher was installed manually