[CI] Renamed ci workflow to build_docker and image tag from `late…

…st` to `nightly` (#242)

* Renamed `ci.yaml` to `build_docker.yaml`

Renamed continuous integration workflow to build docker

* Changed the image tag from `latest` to `nightly`

.github/workflows/ci.yaml → .github/workflows/build_docker.yaml

@@ -1,4 +1,4 @@
-name: continuous integration
+name: build docker
 
 on:
   push:
@@ -29,4 +29,4 @@ jobs:
           context: .
           file: ./Dockerfile
           push: true
-          tags: ${{ secrets.DOCKERHUB_USERNAME }}/api:latest
+          tags: ${{ secrets.DOCKERHUB_USERNAME }}/api:nightly