PG-218: Add Coverall code coverage to pg_stat_monitor.

Added 'Coverall' (https://coveralls.io) code coverage to pg_stat_monitor repo so that in future we don't have to perform this activity manually. Secondly, it will also make sure that code coverage detailed report link and status is readily available on repos github main page for each checkin (PR & Push), eventually helping in development velocity.

.github/workflows/coverage_test.yml

@@ -0,0 +1,68 @@
+name: coverage-test
+on: ["push", "pull_request"]
+
+jobs:
+  build:
+    name: coverage-test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Clone postgres repository
+        uses: actions/checkout@v2
+        with:
+          repository: 'postgres/postgres'
+          ref: 'REL_13_STABLE'
+
+      - name: Clone pg_stat_monitor repository
+        uses: actions/checkout@v2
+        with:
+          path: 'src/pg_stat_monitor'
+          ref: 'master'
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt purge postgresql-client-common postgresql-common postgresql postgresql*
+          sudo apt-get install libreadline6-dev systemtap-sdt-dev zlib1g-dev libssl-dev libpam0g-dev python-dev bison flex libipc-run-perl git lcov -y
+          sudo rm -rf /var/lib/postgresql/
+          sudo rm -rf /var/log/postgresql/
+          sudo rm -rf /etc/postgresql/
+          sudo rm -rf /usr/lib/postgresql
+          sudo rm -rf /usr/include/postgresql
+          sudo rm -rf /usr/share/postgresql
+          sudo rm -rf /etc/postgresql
+          sudo rm -f /usr/bin/pg_config
+      - name: Create pgsql dir
+        run: mkdir -p /opt/pgsql
+
+      - name: Build postgres
+        run: |
+          export PATH="/opt/pgsql/bin:$PATH"
+          ./configure --enable-coverage --enable-tap-tests --prefix=/opt/pgsql
+           make
+           make install
+      - name: Start postgresql cluster
+        run: |
+          export PATH="/opt/pgsql/bin:$PATH"
+          /opt/pgsql/bin/initdb -D /opt/pgsql/data
+          /opt/pgsql/bin/pg_ctl -D /opt/pgsql/data -l logfile start
+      - name: Build pg_stat_monitor
+        run: |
+          export PATH="/opt/pgsql/bin:$PATH"
+          sudo cp /opt/pgsql/bin/pg_config /usr/bin
+          make USE_PGXS=1
+          make USE_PGXS=1 install 
+        working-directory: src/pg_stat_monitor/
+
+      - name: Start pg_stat_monitor_tests & Run code coverage 
+        run: |
+          /opt/pgsql/bin/pg_ctl -D /opt/pgsql/data -l logfile stop
+          echo "shared_preload_libraries = 'pg_stat_monitor'" >> /opt/pgsql/data/postgresql.conf
+          /opt/pgsql/bin/pg_ctl -D /opt/pgsql/data -l logfile start
+          make installcheck
+          make coverage-html
+          lcov --capture --directory . --output-file coverage/lcov.info
+          pip install cpp-coveralls
+          export COVERALLS_REPO_TOKEN="${{ secrets.COVERALL_PG_STAT_MONITOR_TOKEN }}"
+          coveralls --verbose
+        working-directory: src/pg_stat_monitor/
+