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This adds a new middleware dealing with a new /composerize API endpoint.

Following routes are registered with this patch:

• GET /composerize: Generates the extension composer name map
• POST /composerize/{key}: Generates a composer.json file for the given extension key

The middleware is easily extensible. New routes can be added in the $routes array,
by defining the endpoint (including the route parameters) and the allowed HTTP method.

The request will automatically be forwarded to the ComposerizeController request
handler, containing the PSR-7 request object, which is extended with the full routeResult.

Closes #515 (closed)