Add back spring-cloud-function-web (faster startup)

With this change there are now 2 choices for web endpoints. The
stream servlet binder is useful for multi-binder use cases
(e.g. HTTP -> message broker).

spring-cloud-function-web/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -0,0 +1,9 @@
+{"properties": [
+  {
+    "name": "spring.cloud.function.web.path",
+    "type": "java.lang.String",
+    "description": "Path to web resources for functions (should start with / if not empty).",
+    "defaultValue": ""
+  }]
+}
+

spring-cloud-function-web/src/main/resources/META-INF/spring.factories

@@ -0,0 +1,2 @@
+org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
+org.springframework.cloud.function.web.flux.ReactorAutoConfiguration