adds publish to Hex GitHub action

.github/workflows/elixir.yml

@@ -6,6 +6,7 @@
 name: Elixir CI
 
 on:
+  [workflow_call]  # allow this workflow to be called from other workflows
   push:
     branches: [ "main" ]
   pull_request:

.github/workflows/hex.yml

@@ -0,0 +1,18 @@
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  build:
+    uses: ./.github/workflows/elixir.yml
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out
+        uses: actions/checkout@v3
+
+      - name: Publish to Hex.pm
+        uses: erlangpack/github-action@v3
+        env:
+          HEX_API_KEY: ${{ secrets.HEX_API_KEY }}