Automate release on PyPi (#4015)

.github/config/pypi-release-slack-notification.yml

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+pretext: Triggered via {{eventName}} of {{env.VERSION}} by {{actor}}
+title: "Haystack PyPi release"
+
+text: |
+  <https://pypi.org/project/farm-haystack/{{env.VERSION}}/|PyPi release {{env.VERSION}}>
+
+  {{#if (eq jobStatus "SUCCESS")}}
+    Haystack {{env.VERSION}} has been released on PyPi :rocket:
+  {{else if (eq jobStatus "FAILURE")}}
+    {{icon jobStatus}} Haystack {{env.VERSION}} PyPi release failed! {{icon jobStatus}}
+  {{else if (eq jobStatus "CANCELLED")}}
+    {{icon jobStatus}} Haystack {{env.VERSION}} PyPi release has been cancelled! {{icon jobStatus}}
+  {{/if}}
+
+fallback: |-
+  Haystack {{env.VERSION}} PyPi release status: {{jobStatus}}
+
+footer: >-
+  <{{repositoryUrl}}|{{repositoryName}}> <{{workflowRunUrl}}|{{workflow}} #{{runNumber}}>
+
+colors:
+  success: "#5DADE2"
+  failure: "#884EA0"
+  cancelled: "#A569BD"
+  default: "#7D3C98"
+
+icons:
+  success: ":white_check_mark:"
+  failure: ":x:"
+  cancelled: ":interrobang:"
+  skipped: ":interrobang:"
+  default: ":interrobang:"

.github/workflows/pypi_release.yml

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+name: Project release on PyPi
+
+on:
+  tags:
+    - "v[0-9].[0-9]+.[0-9]+*"
+
+jobs:
+  release-on-pypi:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Hatch
+        run: pip install hatch
+
+      - name: Build Haystack
+        run: hatch build
+
+      - name: Publish on PyPi
+        env:
+          HATCH_INDEX_USER: __token__
+          HATCH_INDEX_AUTH: ${{ secrets.PYPI_API_TOKEN }}
+        run: hatch publish -y
+
+      - name: Notify Slack
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+        if: always()
+        uses: act10ns/slack@v2
+        with:
+          status: ${{ job.status }}
+          channel: "#haystack"
+          config: .github/config/pypi-release-slack-notification.yml