Vertx lifecycle hook for VertxBuilder customization

[tsegismont]

Given methods like TracingOptions#setTracer have been deprecated, a new hook can help users configure the Vert.x instance.

[tsegismont]

For now, just a draft for discussion.

@vietj it's not possible to use the public builder here without breaking the command launcher API.

If we introduce this new method in Vert.x 4, it's going to change a little bit in Vert.x 5. A little change, but still a breaking one, that we need to be aware of.

If we agree on doing this, I'll add a test to the PR

[vietj]

I'm good for a breaking change here given it's an API that fades away in 5

[tsegismont]

@vietj PTAL