fix: add Docker Hub login before building image (#29)

# Motivation

The Docker image build is failing with authentication error:
```
401 Unauthorized
{"details":"access token has insufficient scopes"}
```

This prevents the Docker image from being published to Docker Hub.

# Description

## Root Cause

The Jib Maven plugin needs Docker Hub credentials to push images. It was
trying to use credentials from the Docker config file
(`~/.docker/config.json`), but this file didn't exist or didn't have
valid credentials.

The error message indicates that Jib couldn't authenticate:
```
Build image failed, perhaps you should make sure your credentials for 
'registry-1.docker.io/dockerhubaneo/armonik-dynamic-java-worker' are set up correctly
```

## Solution

Add an explicit Docker login step before building the image:

```yaml
      - name: Log in to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ secrets.DOCKER_HUB_LOGIN }}
          password: ${{ secrets.DOCKER_HUB_TOKEN }}
```

This creates credentials in `~/.docker/config.json` that Jib
automatically reads when pushing images.

Author: aneojgurhem

.github/workflows/release.yml

@@ -133,16 +133,19 @@ jobs:
           java-version: '17'
           cache: maven
 
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_HUB_LOGIN }}
+          password: ${{ secrets.DOCKER_HUB_TOKEN }}
+
       - name: Set project version
         working-directory: worker
         run: ./mvnw -B -ntp versions:set -DnewVersion=${{ needs.extract-version.outputs.version }} -DprocessAllModules=true -DgenerateBackupPoms=false
 
       - name: Build and push Docker image
         working-directory: worker
         run: ./mvnw -B -ntp clean package -Pdocker
-        env:
-          DOCKER_USERNAME: ${{ secrets.DOCKER_HUB_LOGIN }}
-          DOCKER_PASSWORD: ${{ secrets.DOCKER_HUB_TOKEN }}
 
       - name: Verify Docker image
         run: |