cmd-diff: support git difftool so we can utilize vimdiff

Having vimdiff is a lot more powerful to me because you can manually
do a few things in the terminal to massage the files on each side of the
diff to give you more information (i.e. narrow in on exactly what diff
you are interested in). Let's add a --difftool boolean flag to trigger
`git difftool`, which will allow diffs to be displayed using vimdiff.

Additionally include vim-enhanced so we have `vimdiff` installed and
at our disposal.

Author: dustymabe

src/cmd-diff

@@ -54,11 +54,20 @@ TMP_REPO = 'tmp/repo'
 
 DIFF_CACHE = 'tmp/diff-cache'
 
+# Global variable that can be set once and direct the underlying code to leverage
+# a difftool with git diffing or not. This could be an argument passed around to
+# underlying functions, but decided to just implement it as a global variable for now.
+USE_DIFFTOOL = False
+
 
 def main():
     args = parse_args()
     builds = Builds()
 
+    # Modify the USE_DIFFTOOL global based on the --difftool argument
+    global USE_DIFFTOOL
+    USE_DIFFTOOL = args.difftool
+
     latest_build = builds.get_latest()
 
     os.makedirs(DIFF_CACHE, exist_ok=True)
@@ -114,6 +123,7 @@ def parse_args():
     parser.add_argument("--to", dest='diff_to', help="Second build ID")
     parser.add_argument("--gc", action='store_true', help="Delete cached diff content")
     parser.add_argument("--arch", dest='arch', help="Architecture of builds")
+    parser.add_argument("--difftool", action='store_true', help="Use git difftool")
 
     for differ in DIFFERS:
         parser.add_argument("--" + differ.name, action='store_true', default=False,
@@ -424,7 +434,10 @@ def diff_cmd_outputs(cmd, path_from, path_to, strategy: DiffCmdOutputStrategy =
 
 
 def git_diff(arg_from, arg_to):
-    runcmd(['git', 'diff', '--no-index', arg_from, arg_to], check=False)
+    subcmd = 'diff'
+    if USE_DIFFTOOL:
+        subcmd = 'difftool'
+    runcmd(['git', subcmd, '--no-index', arg_from, arg_to], check=False)
 
 
 def cache_dir(dir):

src/deps.txt

@@ -111,3 +111,6 @@ python3-libguestfs
 
 # For generating kubernetes YAML files (e.g Konflux resources)
 kustomize
+
+# For vimdiff
+vim-enhanced