Break out sse into a compile unit

Verify similar to beb96b0 Break out websockets

Break out the SSE functions into a separate compile unit.  This allows
the SSE sockets in beast to be compiled separately, which significantly
reduces the overall compile time by a few seconds.  Code is identical
with the exceptions of minor header definitions to convert header-only
to compile unit.

Change-Id: I5aae4f17cbd2badf75b3e0bb644a2309f6300663
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/meson.build b/meson.build
index 9eb5488..54f7cde 100644
--- a/meson.build
+++ b/meson.build
@@ -367,6 +367,7 @@
 
 srcfiles_bmcweb = files(
     'http/mutual_tls.cpp',
+    'http/routing/sserule.cpp',
     'http/routing/websocketrule.cpp',
     'redfish-core/src/dbus_log_watcher.cpp',
     'redfish-core/src/error_message_utils.cpp',