RS: Add banner to RS 7.4 versioned docs (#895)

Author: rrelledge

content/operate/rs/7.4/_index.md

@@ -10,6 +10,8 @@ hideListLinks: true
 weight: 10
 url: '/operate/rs/7.4/'
 linkTitle: 7.4
+bannerText: This documentation applies to Redis Software versions 7.4.x.
+bannerChildren: true
 ---
 
 [Redis Enterprise](https://redis.io/enterprise/) is a self-managed, enterprise-grade version of Redis.