Add kapa.ai integration to website (#6490)

Author: hadley

_pkgdown.yml

@@ -7,6 +7,20 @@ template:
   includes:
     in_header: |
       <script defer data-domain="ggplot2.tidyverse.org,all.tidyverse.org" src="https://plausible.io/js/plausible.js"></script>
+      <script async src="https://widget.kapa.ai/kapa-widget.bundle.js"
+      data-button-hide="true"
+      data-modal-disclaimer="This is a custom LLM for answering questions about dplyr, tidyr, and ggplot2. Answers are based on the contents of the documentation. Rate the answers to let us know what you think!"
+      data-modal-ask-ai-input-placeholder="Ask me a question about dplyr, tidyr, or ggplot2."
+      data-modal-header-bg-color="#f9f9f9"
+      data-modal-override-open-class="open-kapa-widget"
+      data-project-color="#365a7a"
+      data-project-name="ggplot2"
+      data-modal-title="tidyverse AI ✨"
+      data-project-logo="https://avatars.githubusercontent.com/u/22032646?s=200&u=235532df5cf8543246812f73db051b793f868807&v=4"
+      data-user-analytics-fingerprint-enabled="true"
+      data-bot-protection-mechanism="hcaptcha"
+      data-website-id="5dcac24a-bd5a-4874-9f5b-3341afddd8c3"
+      ></script>
 
 development:
   mode: auto
@@ -25,7 +39,7 @@ home:
   links:
   - text: Learn more
     href: https://r4ds.had.co.nz/data-visualisation.html
-  - text: Extensions
+  - text: Extensions 🧩
     href: https://exts.ggplot2.tidyverse.org/gallery/
 
 reference:
@@ -300,7 +314,13 @@ news:
 navbar:
   structure:
     left: [intro, reference, news, articles, extensions]
+    right: [search, github, ai]
   components:
     extensions:
-      text: Extensions
+      icon: fa-puzzle-piece
+      aria-label: Extensions
       href: https://exts.ggplot2.tidyverse.org/gallery/
+    ai:
+      text: Ask AI ✨
+      href: "#"
+      class: open-kapa-widget