String extractDynamicIndexPatternStr(String index) {
			int start = index.indexOf("{");
			int end = index.lastIndexOf("}");
			return index.substring(start, end + 1);
		}
Extract dynamic index pattern string from index pattern string.
elasticsearch7/elasticsearch7-sink/src/main/java/org/apache/flink/streaming/connectors/elasticsearch/index/IndexGeneratorFactory.java