run CI more frequently

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/193

- Add daily CI.
- rename `Unit Test` to `CI`.
- rename the `build` to `python-unittest`.

Reviewed By: tglik

Differential Revision: D35102575

fbshipit-source-id: cbcc3992e019d3e00d8e862b81de4bb1c16f8fe1

.github/workflows/unit_test.yml → .github/workflows/workflows.yaml

-name: Unit Test
+name: CI
 
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: "0 0 * * *"  # @daily
 
 jobs:
-  build:
+  python-unittest:
 
     runs-on: ubuntu-latest