[SPE-6] Boundary vs. other software (#2626)

* [SPE-6] Boundary vs. other software

* Minor edit for word choice

* Update navigation

* Change redundant word in nav

* Fix broken links

* Add anchor link

* Copy edits

* Nest navigation for What is Boundary? section

* Apply batch suggestions from code review

Co-authored-by: Adam Bouhmad <adbouhmad@gmail.com>

* Update intro sentence with new wording

* Split sections out into topics

* changes title of Introduction -> Overview to What is Boundary?

* adds redirects for use-cases and what-is-boundary

Co-authored-by: Adam Bouhmad <adbouhmad@gmail.com>
Co-authored-by: stellarsquall <stellarsquall@protonmail.ch>

website/data/docs-nav-data.json

@@ -1,11 +1,49 @@
 [
   {
-    "title": "What is Boundary?",
-    "path": "what-is-boundary"
-  },
-  {
-    "title": "Use Cases",
-    "path": "use-cases"
+    "title": "Introduction",
+    "routes": [
+      {
+        "title": "What is Boundary?",
+        "path": "overview/what-is-boundary"
+      },
+      {
+        "title": "Use Cases",
+        "path": "overview/use-cases"
+      },
+      {
+        "title": "Boundary vs. Other Software",
+        "routes": [
+          {
+            "title": "Overview",
+            "path": "overview/vs/other-software"
+          },
+          {
+            "title": "Zero Trust",
+            "path": "overview/vs/zero-trust"
+          },
+          {
+            "title": "Bastion Hosts",
+            "path": "overview/vs/bastion-hosts"
+          },
+          {
+            "title": "VPNs",
+            "path": "overview/vs/vpn"
+          },
+          {
+            "title": "Privileged Access Management",
+            "path": "overview/vs/pam"
+          },
+          {
+            "title": "Software Defined Perimeter",
+            "path": "overview/vs/sdp"
+          },
+          {
+            "title": "Secrets Management Tools",
+            "path": "overview/vs/secrets-management"
+          }
+        ]
+      }
+    ]
   },
   {
     "title": "Getting Started",