Document how to serve static resources not defined at startup

[gsmet]

Take the following case:

• the application uploads images in a directory
• you want to serve the images from this directory

Ideally you would use a Vert.x router to serve the images and this needs to be documented (also, we need to document the fact that you should NOT upload your resources to META-INF/resources).

See https://stackoverflow.com/questions/76530777/serving-images-static-files-from-quarkus-is-failing-on-server for more context.

[maxandersen]

+1

related to #33222 about having a way to automatically pick up an implicit location to serve static resources which could then be served more efficiently. This would be complementary and have it documented how to do it explicilty is definitely good.

[dvsingh9]

@gsmet this documentation should be part of https://github.com/quarkusio/quarkus/blob/main/docs/src/main/asciidoc/vertx-reference.adoc?plain=1#L882
Another section talking about serving static resource ?

[dvsingh9]

#36157 for review