Add nightly tag to container image build CI (#1282)

## Description

Pushes `nightly` as the tag for latest images.

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [x] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor

## Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #<issue>

## Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

.github/workflows/ci.yml

@@ -346,6 +346,7 @@ jobs:
           tags: |
             type=ref,event=tag
             type=sha,format=short,prefix=
+            type=raw,value=nightly
 
       # deploy the image
       - name: Build image and push to GitHub Container Registry