Add get-tags and count-tags scripts

Add `get-tags` and `count-tags` scripts to get and count Git tags within
a repository, including the ability to filter tags - e.g. only get or
count tags that begin with a certain date.

home-manager/opdavies/PW05CH3L.nix

@@ -38,7 +38,9 @@
   };
 
   home.packages = with pkgs; [
+    count-tags
     create-script
+    get-tags
     tag-release
     time-until
     update-all-git-repos

home-manager/opdavies/t480.nix

@@ -99,8 +99,10 @@
   home.packages = with pkgs; [
     backup-websites
     build-glove80
+    count-tags
     create-script
     displayselect
+    get-tags
     qrencode
     mounter
     move-firefox-screenshots