GH-195: Introduce ComponentCustomizer (#273)

Fixes #195 

* Introduce a `ComponentCustomizer` contract to be exposed in
the end-user configuration for particular bean type
* introduce a `@CustomizationAware` annotation to mark a component 
as customizable
* Introduce a `ComponentCustomizationBeanPostProcessor` as an auto-configured
bean to apply `ComponentCustomizer` to a matching `@CustomizationAware` (if any)
* Use `@CustomizationAware` in the `FileSupplierConfiguration`
and demonstrate `ComponentCustomizer` feature in its tests
* Move `config-common` to functions parent to make the mentioned auto-configuration
available for all the functions
* Remove some other duplicated dependencies from the affected poms

function/http-request-function/pom.xml

@@ -19,13 +19,6 @@
     </properties>
 
     <dependencies>
-
-        <dependency>
-            <groupId>org.springframework.cloud.fn</groupId>
-            <artifactId>config-common</artifactId>
-            <version>${project.version}</version>
-        </dependency>
-
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-webflux</artifactId>