Documentation and test code movement around topology

As a part of #8512 I need to have a much more clear understanding of the
topology construct of vector than I presently do. I have an eye toward
accomplishing some of the aims of the Architecture Revisit RFC but would like to
get there in small steps.

This commit does not functionally change vector. It moves some test code around
and adjusts the documentation to be more, I hope, clear about what's what.

Signed-off-by: Brian L. Troutwine <brian@troutwine.us>

src/main.rs

@@ -12,10 +12,10 @@ fn main() {
 
 #[cfg(windows)]
 pub fn main() {
-    // We need to be able to run vector in User Interactive mode. We first try to run vector
-    // as a service. If we fail, we consider that we are in interactive mode and then fallback
-    // to console mode.
-    // See https://docs.microsoft.com/en-us/dotnet/api/system.environment.userinteractive?redirectedfrom=MSDN&view=netcore-3.1#System_Environment_UserInteractive
+    // We need to be able to run vector in User Interactive mode. We first try
+    // to run vector as a service. If we fail, we consider that we are in
+    // interactive mode and then fallback to console mode.  See
+    // https://docs.microsoft.com/en-us/dotnet/api/system.environment.userinteractive?redirectedfrom=MSDN&view=netcore-3.1#System_Environment_UserInteractive
     vector::vector_windows::run().unwrap_or_else(|_| {
         let app = Application::prepare().unwrap_or_else(|code| {
             std::process::exit(code);