Adds Endpoint command ref and prebuilt anomaly detection jobs docs

[nastasha-solomon]

NOTE: This PR needs to be merged for the prebuilt anomaly detection jobs refs in elastic/security-docs#6586 to resolve.

Made the following changes:

• Added the Endpoint command ref and prebuilt anomaly detection jobs docs to this repo. (They're being removed from the security-docs repo via Removes Endpoint command ref and prebuilt anomaly detection jobs docs  security-docs#6586)
• Renamed the "Prebuilt jobs" page to "Prebuilt anomaly detection jobs" for clarity.
• Updated the reference TOC so it now includes the "Endpoint command reference" and "Prebuilt anomaly detection jobs" pages.
• Updated the list of features on the Security reference landing page.

Previews:

• Security index page: Updated the list of features
• Endpoint command reference
• Prebuilt anomaly detection jobs

[jmikell821]

Looks great, @nastasha-solomon, thanks for pulling this together! Just left one optional suggestion.