[CI] Re-add Apps plugin milestone workflow

Github action is named strangely in UI. Re-adding to fix display name.

.github/workflows/apps-plugin-milestone.yml

@@ -0,0 +1,74 @@
+name: Apps Plugin (Milestone)
+
+on:
+  workflow_dispatch:
+    inputs:
+      milestoneVersion:
+        description: "Milestone version (ex: '-M1')"
+        required: true
+
+env:
+  MAVEN_THREADS: '-T 0.5C'
+
+jobs:
+  build:
+    if: ${{ github.repository == 'spring-cloud/stream-applications' }}
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: spring-cloud-dataflow-apps-plugin
+    steps:
+      - uses: actions/checkout@v2
+                - uses: actions/setup-java@v3
+                with:
+                  java-version: 17
+                  distribution: temurin
+      - uses: jvalkeal/setup-maven@v1
+        with:
+          maven-version: 3.8.8
+          maven-mirror: 'https://dlcdn.apache.org/maven/maven-3/'
+      - uses: jfrog/setup-jfrog-cli@v1
+        with:
+          version: 1.46.4
+        env:
+          JF_ARTIFACTORY_SPRING: ${{ secrets.JF_ARTIFACTORY_SPRING }}
+      - uses: actions/cache@v2
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-m2-
+      - name: Configure JFrog Cli
+        run: |
+          jfrog rt mvnc \
+            --server-id-resolve=repo.spring.io \
+            --server-id-deploy=repo.spring.io \
+            --repo-resolve-releases=libs-milestone \
+            --repo-resolve-snapshots=libs-snapshot \
+            --repo-deploy-releases=libs-milestone-local \
+            --repo-deploy-snapshots=libs-snapshot-local
+          echo JFROG_CLI_BUILD_NAME=spring-cloud-dataflow-apps-plugin-main-milestone >> $GITHUB_ENV
+          echo JFROG_CLI_BUILD_NUMBER=$GITHUB_RUN_NUMBER >> $GITHUB_ENV
+      - name: Build and Publish
+        run: |
+          jfrog rt mvn build-helper:parse-version versions:set \
+            -gs settings.xml \
+            -Pstagingmilestone \
+            -DprocessAllModules=true \
+            -DgenerateBackupPoms=false \
+            -Dartifactory.publish.artifacts=false \
+            -DnewVersion='${parsedVersion.majorVersion}.${parsedVersion.minorVersion}.${parsedVersion.incrementalVersion}-'${milestoneVersion} \
+            -B
+          jfrog rt build-clean
+          jfrog rt mvn -gs settings.xml -Pstagingmilestone,full,deploymentfiles -B install -DskipTests
+          jfrog rt build-publish
+          echo spring_cloud_dataflow_apps_plugin_version=$(mvn help:evaluate -Dexpression=project.version -q -DforceStdout) >> $GITHUB_ENV
+      - name: Tag Release
+        uses: jvalkeal/[email protected]
+        with:
+          tag-release-branch: ${{ env.spring_cloud_dataflow_apps_plugin_version }}
+          tag-release-tag: ${{ env.spring_cloud_dataflow_apps_plugin_version }}
+          tag-release-tag-prefix: v
+      - name: Clean cache
+        run: |
+          find ~/.m2/repository -type d -name '*SNAPSHOT' | xargs rm -fr