Use unique Duo Chat icon on CTAs on GitLab

Context

This issue related to #470637 (closed), which proposes adding a unique icon for GitLab Duo Chat in the IDE. This issue is also related to an initiative to make AI feature CTAs and AI feature onboarding more consistent.

Problem to solve

Click to see problem to solve

Image	Description
	It's important to clearly communicate what a feature will do so the user can make an informed choice if they would like to engage with the feature.
	We do not do a good job setting user expectations on the CTA of AI features. How would the user know what each of these CTAs do?

Related data an UXR

• AI features usage data
• Learnability of new features UXR

Proposal

Image	Description
	Replace existing icon with new duo chat icon
	When the button is disabled, use the duo chat off icon

Implementation

Web

• GitLab Duo Chat → !163080 (merged)
• Explain vulnerability → (Skipping) #473396 (comment 2071282080)
• (RCA) Troubleshoot → !164248 (merged)

IDE Extensions

• GitLab Duo Chat (JetBrains) → gitlab-org/editor-extensions/gitlab-jetbrains-plugin#610 (closed)
• GitLab Duo Chat (VS Code) → gitlab-vscode-extension#1514 (closed) → gitlab-vscode-extension!1873 (merged)

Next steps (FYI only, after this issue)

Click to see vision

1. Better set user expectations by differentiating Chat CTAs from other AI CTAs. Develop a standard UI treatment for a Chat CTA in GitLab. (this issue)
2. All GitLab chat CTAs align to the standard defined by this issue (many issues)
3. When all features have a standard CTA, we can develop standard for onboarding and feature discoverability of chat features ( #460072 (closed)). This will help address the pain points from the UXR around learning about new features.

Standardizing the chat CTA opens the door for other potential UX improvements:

Image	Description	Issue
	If we have a standard for Chat CTAs, we can also develop a standard for onboarding to chat features	#460072 (closed)