Task A-2: Storing latest tag in .env file + Task A-8: Prefix branch name

Refer to details in cleanup issue:
Task A-2: e-mission/e-mission-docs#1082 (comment)

Storing latest tag as well so that artifacts are not needed.

For now not removing artifacts until the internal script is updated to handle this change.

----

Task A-8: Prefixing branch name to the docker tag along with the date.
In the internal script we will not need to maintain the different branch lists as the images will be completely tagged in the external workflows themselves.
We can simply use the tags without modifications then.

For now, not prefixing the tag to the artifact since we will be removing the artifact anyways.
And current internal script works with artifacts.
Once I update the internal script, will come back and remove artifacts.

.env

@@ -0,0 +1 @@
+JOIN_IMAGE_TAG=2024-08-21--29-53

.github/workflows/image_build_push.yml

@@ -17,6 +17,14 @@ jobs:
     steps:
 
     - uses: actions/checkout@v2
+
+    - name: Set docker image tags
+      id: set-tags
+      run: |
+        set -a; source .env; set +a
+        echo "JOIN_IMAGE_TAG=${JOIN_IMAGE_TAG}" >> "$GITHUB_OUTPUT"
+        echo "Current join-page image tag (push): ${JOIN_IMAGE_TAG}"
+
     - name: docker login
       run: | # log into docker hub account
         docker login -u $DOCKER_USER -p $DOCKER_PASSWORD
@@ -37,6 +45,22 @@ jobs:
       run: |
         docker push $DOCKER_USER/${GITHUB_REPOSITORY#*/}:${GITHUB_REF##*/}_${{ steps.date.outputs.date }}
 
+    - name: Update .env file 
+      run: |
+        echo "JOIN_IMAGE_TAG=${GITHUB_REF##*/}_${{ steps.date.outputs.date }}" > .env
+
+    - name: Add, Commit, Push changes to .env file
+      run: |
+        git config --local user.email "[email protected]"
+        git config --local user.name "Github Actions bot to update .env with latest tags"
+        if git diff --quiet; then
+          echo "Latest timestamp already present in .env file, no changes to commit"
+        else
+          git add .env
+          git commit -m "Updated docker image tags in .env file to the latest timestamp"
+          git push origin 
+        fi
+
     - name: Create artifact text file
       run: |
           echo ${{ steps.date.outputs.date }} > join_page_tag_file.txt