Add qlpack.json files

Eventually these files will subsume the current `queries.xml` files
at the top of query-containing and library directories. For now they're
just here to support internal testing of the tooling support for them
we're writing on.

Format and contents is a work in progress. If you're not in Semmle,
don't depend on anything here making sense (or staying stable) until
you see the version tags increase to something nonzero.

cpp/ql/src/qlpack.json

@@ -0,0 +1,5 @@
+{
+    "name": "codeql-cpp",
+    "version": "0.0.0",
+    "dbscheme": "semmlecode.cpp.dbscheme"
+}