[FEATURE] Custom Middleware Extensibility: Allow multiple definitions…

… of the same custom middleware

Similar to the implementation for custom tasks:
https://github.com/SAP/ui5-builder/blob/d60c67dafc6d96a8345da2004972cd4b839eece6/lib/types/AbstractBuilder.js#L81-L89

Resolves #222

lib/middleware/MiddlewareManager.js

@@ -154,12 +154,17 @@ class MiddlewareManager {
 					`defines neither a "beforeMiddleware" nor an "afterMiddleware" parameter. One must be defined.`);
 			}
 
+			let middlewareName = middlewareDef.name;
 			if (this.middleware[middlewareDef.name]) {
 				// Middleware is already known
-				throw new Error(`Failed to add custom middleware ${middlewareDef.name}. ` +
-					`A middleware with the same name is already known.`);
+				// => add a suffix to allow for multiple configurations of the same middleware
+				let suffixCounter = 0;
+				while (this.middleware[middlewareName]) {
+					suffixCounter++; // Start at 1
+					middlewareName = `${middlewareDef.name}--${suffixCounter}`;
+				}
 			}
-			await this.addMiddleware(middlewareDef.name, {
+			await this.addMiddleware(middlewareName, {
 				wrapperCallback: (middleware) => {
 					return ({resources}) => {
 						const options = {