docs: bundle assets with Hugo

Also:

* load any docs' third-party dependencies from node_modules (except for examples)
* exclude docsearch from layouts that don't use it
* preconnect to algolia only when not examples layout
* switch to `RelPermalink`
* refactor JS assets into partials

hugo.yml

@@ -8,8 +8,6 @@ security:
     getenv:
       - ^HUGO_
       - NETLIFY
-  gotemplates:
-    allowActionJSTmpl: true
 
 markup:
   goldmark:
@@ -21,6 +19,9 @@ markup:
     startLevel:         2
     endLevel:           6
 
+build:
+  noJSConfigInAssets:   true
+
 buildDrafts:            true
 buildFuture:            true
 
@@ -44,6 +45,8 @@ module:
       target:           layouts
     - source:           site/static
       target:           static
+    - source:           node_modules/@docsearch/css
+      target:           assets/scss/@docsearch/css
     - source:           site/static/docs/5.3/assets/img/favicons/apple-touch-icon.png
       target:           static/apple-touch-icon.png
     - source:           site/static/docs/5.3/assets/img/favicons/favicon.ico