refactor: only use detected port mapping if override is not specified

Previously, we would always set the port mapping during a dockerfile build, making it difficult for users to override mappings. We also only _sometimes_ updated the detected port mapping, further confusing issues when users were migrating from Dockerfile to Buildpacks for builds.

Now, we always detect the port mapping during the build process, and only use that detected port mapping if an override is not specified. This greatly simplifies the experience around port mapping, as now a user can create an app, set a port mapping, and that first deploy will respect the port mapping without an additional deploy.

The builder always has the best context for what the app should be listening on, and thus we can always specify a "default" port mapping at this stage. Users can override this map as desired later.

This change also results in the removal of a ton of internal code that is now centralized in the ports plugin.

Closes #4067

plugins/builder-lambda/builder-build

@@ -36,7 +36,9 @@ trigger-builder-lambda-builder-build() {
     cp "$SOURCECODE_WORK_DIR/Procfile" "${DOKKU_LIB_ROOT}/data/builder-lambda/$APP/$GIT_REV.Procfile"
   fi
 
-  plugn trigger ports-set-detected "$APP" "http:80:5000"
+  # ensure we have a port mapping
+  plugn trigger ports-configure "$APP"
+  plugn trigger ports-set-detected "$APP" "http:$(plugn trigger ports-get-property "$APP" proxy-port):5000"
   plugn trigger post-build-lambda "$APP"
 }