feat(ci): add tag script (#263)

`make tag` will create a tag based on the version found in
`lua/kulala/globals/init.lua` which resembles a string like
`v88.84.20091105` and pushes it to the origin remote.

It will fail,

- if the tag already exists
- if you're not on the main branch
- if you're git status is dirty

Makefile

@@ -1,2 +1,4 @@
 version:
 	./scripts/set-version.sh $(VERSION)
+tag:
+	./scripts/tag.sh

scripts/tag.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+
+# Creates a tag based on the version found in lua/kulala/globals.lua
+# and pushes it to the remote repository.
+
+set -euo pipefail
+
+get_tag() {
+  local file="./lua/kulala/globals/init.lua"
+  local VERSION_REGEX="VERSION = \"([0-9]+\.[0-9]+\.[0-9]+)\""
+  local version
+  version=$(grep -oP "$VERSION_REGEX" "$file" | cut -d'"' -f2)
+  echo "v$version"
+}
+
+check_on_main_branch() {
+  local branch
+  branch=$(git branch --show-current)
+  if [ "$branch" != "main" ]; then
+    echo "You must be on the main branch to create a tag."
+    exit 1
+  fi
+}
+
+check_if_clean() {
+  if ! git diff --quiet; then
+    echo "You have uncommitted changes. Please commit or stash them before creating a tag."
+    exit 1
+  fi
+}
+
+check_on_main_branch
+check_if_clean
+
+tag=$(get_tag)
+
+git tag "$tag" && git push origin "$tag"