apacheGH-45230: [Docs] Add LinkedIn social link and fix top nav scaling problems (apache#45228)

This adds a LinkedIn icon social link to the main docs pages and fixes the layout of the top nav, which previously looked bad
at widths between 960px and 1200px.

* GitHub Issue: apache#45230

Author: ianmcook

docs/source/_static/theme_overrides.css

@@ -25,14 +25,39 @@
   --pst-font-weight-heading: 600;
 }
 
-/* Change header hight to make the logo a bit larger */
+/* Change header height to make the logo a bit larger */
 /* only on wider screens */
-@media only screen and (min-width: 1170px){
+
+@media only screen and (min-width: 1200px) {
   :root {
     --pst-header-height: 6rem;
   }
 }
 
+/* Adjust layout of nav to fit narrower screens */
+
+@media only screen and (max-width: 1199px) {
+
+  /* Condense link text in nav to preserve layout */
+  .navbar-header-items__center a.nav-link:not(.dropdown-item),
+  .navbar-header-items__center button.nav-item {
+    letter-spacing: -0.02em;
+  }
+
+  /* Shrink search button */
+  .search-button__default-text,
+  .search-button__kbd-shortcut {
+    display:none !important;
+  }
+
+  /* Reduce horizontal space between icons in nav and sidebar */
+  div.sidebar-header-items__end,
+  div.navbar-header-items__end,
+  ul.navbar-icon-links {
+    column-gap: 0.75rem !important;
+  }
+}
+
 /* Contributing landing page overview cards */
 
 .contrib-card {
@@ -84,3 +109,9 @@ dl.cpp.enumerator {
 p.breathe-sectiondef-title {
   margin-top: 1rem;
 }
+
+/* Keep social icons arranged horizontally in sidebar */
+
+.sidebar-header-items__end {
+  flex-wrap: wrap;
+}

docs/source/conf.py

@@ -342,13 +342,19 @@
     },
     "header_links_before_dropdown": 2,
     "header_dropdown_text": "Implementations",
+    "navbar_align": "left",
     "navbar_end": ["version-switcher", "theme-switcher", "navbar-icon-links"],
     "icon_links": [
         {
             "name": "GitHub",
             "url": "https://github.com/apache/arrow",
             "icon": "fa-brands fa-square-github",
         },
+        {
+            "name": "LinkedIn",
+            "url": "https://www.linkedin.com/company/apache-arrow/",
+            "icon": "fa-brands fa-linkedin",
+        },
         {
             "name": "X",
             "url": "https://twitter.com/ApacheArrow",