adding the banner of webinar 0819 (#668)

* adding the banner of webinar 0819

* Update webinar label and add new announcement headline

* Update index.json

Author: snowlynwang-art

homepage/index.json

@@ -3,6 +3,10 @@
   "label": "Our Journey to 35K+ GitHub Stars: The Real Story of Building Milvus from Scratch",
   "link": "https://milvus.io/blog/journey-to-35k-github-stars-story-of-building-milvus-from-scratch.md",
   "headlines": [
+    {
+      "label": "Webinar: Faster and More Powerful Full-Text Search with Milvus 3.0 | Live on August 19",
+      "link": "https://zilliz.com/event/faster-more-powerful-full-text-search-milvus-3-0"
+    },
     {
       "label": "Announcing Milvus 3.0: Lake-Native Vector Search, S3-based storage, and a More Powerful Retrieval Engine",
       "link": "https://milvus.io/blog/announcing-milvus-3-lake-native-vector-search-and-a-more-powerful-retrieval-engine.md"