Promote the usage of the Maven wrapper in the instructions

[jnizet]

This makes sure everyone (hopefully) uses the same, correct Maven version, makes it easier to setup the development environment and to contribute.

[geoand]

@jnizet This is a great idea IMHO, but I think that it will cause confusion because currently our generated projects don't include the maven wrapper.
Would you like to augment the PR to add the wrapper as well?
See this and this

[jnizet]

I'll have a look tomorrow. But could you explain what these generated projects are, and how, when and where they are generated?
I found it weird to have the Maven wrapper in the main project, but not to tell contributors to use it: that defeats the whole purpose of having the wrapper.

[geoand]

@jnizet Sorry, I thought the PR was about the guides, not Quarkus itself! My bad :(!
Please consider my comment above as it never happened.

Although you did give me an idea to add that wrapper to the quickstarts and the created projects :)

[gsmet]

Makes sense. Thanks.