[Security Solution] Load rules callout copy change

[approksiu]

Summary

We need to update the text on this screen to reflect the current terminology. Rules -> Installed rules (empty state)

Header: "Load Elastic prebuilt detection rules" -> "Install Elastic prebuilt detection rules"

Text: "Elastic Security comes with prebuilt detection rules that run in the background and create alerts when their conditions are met. Select which rules you want to install and enable."

[approksiu]

@nastasha-solomon please check the copy above, I want to make it clearer and point to rules installation.

[elasticmachine]

Pinging @elastic/security-detection-rule-management (Team:Detection Rule Management)