Add STL cgmanifest entry for Boost (#2598)

With SHA for the boost-1.66.0 tag, which is the version from which we made the nuget that we use to build the STL's special math function satellite.

This is a dual of MSVC-PR-382487.

docs/cgmanifest.json

@@ -1,5 +1,14 @@
 {
     "Registrations": [
+        {
+            "component": {
+                "type": "git",
+                "git": {
+                    "repositoryUrl": "https://github.com/boostorg/boost",
+                    "commitHash": "b143a5b72075f47307a23e680889d8434c8afc54"
+                }
+            }
+        },
         {
             "component": {
                 "type": "git",