Add Pipeline Builder foundational agent

What does this MR do and why?

Add Pipeline Builder foundational agent

• Add Pipeline Builder agent definition with catalog ID 1004583
• Add feature flag foundational_pipeline_authoring_agent (disabled by default)
• Add feature flag check in foundational chat agents resolver
• Add documentation for Pipeline Builder agent
• Rename agent from "Pipeline Authoring" to "Pipeline Builder" across docs, definitions, resolver, and specs

Changelog: added

Behind a feature flag. Rollout issue - [FF] `foundational_pipeline_authoring_agent` --... (#588564) • Unassigned

References

Changes in AI Assist repo - chore(dockerfile): add pipeline authoring agent... (gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!4461 - merged) • Rajendra Kadam • 18.9

Screenshots or screen recordings

NA

How to set up and validate locally

NA

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Related to #587460