[DOCS] Elastic Security UI updates

[jmikell821]

A few changes to the security UI:

• New Entity Analytics dashboard [DOCS] Add Entity analytics dashboard  #2517
• New Intelligence section [DOCS] Threat Intelligence - Indicators Page and Indicator Details #2497

[nastasha-solomon]

@jmikell821 I added the intelligence page to the Elastic Security UI topic here. Let me know if you'd prefer for me to revert the change.