Upgrade to Vert.x 4

[malaskowski]

Context Vert.x 4 is coming. Recently, the milestone 4 was released.

Describe the solution you'd like Upgrading to Vert.x 4 will be divided into several phases:

• PoC -> switch dependency to Vert.x 4 and try to estimate how much effort is to switch actually
• Upgrade -> actual upgrade, probably each module will be migrated simultaneously
• Verification -> this must happen after upgrade, probably will include performance testing.

Additional context The PoC phase might be done before Vert.x 4 is released and use some of the milestone builds.