Move Duo Analytics Agent from AI Catalog to Foundational

Problem to solve

The Duo Analytics Agent was added to the AI Catalog. However, longer term, we want this agent to be part of our foundational agents list. This will make the agent available for all customer deployment types, and make it easier to collaborate.

Implementation plan

Follow https://docs.gitlab.com/development/ai_features/foundational_chat_agents/.

In https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist:

1. Create a new prompt definition in AI Gateway
2. Create a new flow config in Duo Workflow Service
3. Create/Update any specs

In https://gitlab.com/gitlab-org/gitlab:

1. Add a new feature flag foundational_analytics_agent
2. Add our agent to the Foundational chat agents resolver, disabling it if the feature flag is off
3. Add our agent to the list of foundational chat agent definitions
4. Create/Update any specs