[Misc] Add flake8 lint workflow. (#4566)

* Add pyproject.toml for autopep8.

* Add pyproject.toml for autopep8.

* Add flake8 annotation in workflow.

* remove

* add

* clean up
Co-authored-by: Steve <ubuntu@ip-172-31-34-29.ap-northeast-1.compute.internal>

.github/workflows/pylint.yml

+name: Lint
+
+on:
+  push:
+    paths:
+      - '*.py'
+
+jobs:
+  flake8_py3:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Setup Python
+        uses: actions/setup-python@v1
+        with:
+          python-version: 3.7.4
+          architecture: x64
+      - name: Checkout PyTorch
+        uses: actions/checkout@master
+      - name: Install flake8
+        run: pip install flake8
+      - name: Run flake8
+        uses: suo/flake8-github-action@releases/v1
+        with:
+          # NOTE: this needs to be the same as the job name.
+          checkName: 'flake8_py3'   
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}