[EuiIcon] Add the Agent Builder icon to EUI Borealis

[isaclfreire]

Problem Statement
Currently, the Agent Builder robot icon is hardcoded in the side nav code of Elasticsearch solution and in the onechat plugin (Agent Builder). As we are working heavily on the migration from current AI Assistants to Agent Builder for 9.3, different solution and teams need to be able to use an official icon.

Urgency
Very urgent, for 9.3 FF (Dec 16th).

Designs or Specs
Here's the Figma file with the latest version of the icon. I am also brunching the Figma Borealis library file next to move it there.