add Micronaut 3 reactive with R2DBC sample project

[pull-vert]

See https://micronaut-projects.github.io/micronaut-data/latest/guide/#r2dbc as exemple (but do not use data-r2dbc).

This task requires #93 because it will use the kotysa-r2dbc Reactor SQL client

Create this project from https://micronaut.io/launch?features=r2dbc&features=h2&features=kotlin-extension-functions&lang=KOTLIN&build=GRADLE

Optional :

• Add &features=test-resources&features=testcontainers URL options for PostgreSQL sample instead of H2
• Use https://micronaut-projects.github.io/micronaut-test-resources/latest/guide/#introduction for tests