Add GitHub Action workflows

Adds the configuration the Gnocchi workflow which moves
the docs, pep8 and functional testing jobs to GitHub Actions.

(cherry picked from commit 1b167c5)

.github/workflows/gnocchi.yml

@@ -0,0 +1,69 @@
+name: Gnocchi
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+# NOTE(tobias-urdin): If you change any jobs make sure to modify
+# the Mergify.io config in .mergify.yml to include the jobs!
+
+jobs:
+  doc:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        env:
+          - docs
+          - docs-gnocchi-web
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: ./.github/actions/gnocchi-container
+        with:
+          command: tox -e ${{ matrix.env }}
+
+  check:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        env:
+          - pep8
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ./.github/actions/gnocchi-container
+        with:
+          command: tox -e ${{ matrix.env }}
+
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python:
+          - py36
+          - py38
+        env:
+          - mysql-ceph-upgrade-from-4.3
+          - postgresql-file-upgrade-from-4.3
+          - mysql-file
+          - mysql-swift
+          - mysql-s3
+          - mysql-ceph
+          - postgresql-file
+          - postgresql-swift
+          - postgresql-s3
+          - postgresql-ceph
+        exclude:
+          - env: mysql-ceph-upgrade-from-4.3
+            python: py36
+          - env: mysql-ceph
+            python: py36
+          - env: postgresql-ceph
+            python: py36
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ./.github/actions/gnocchi-container
+        with:
+          command: tox -e ${{ matrix.python }}-${{ matrix.env }}