Allow consumption of a relational database testcontainer through R2DBC

R2DBC is an initiative to establish a reactive API for relational database integration. It would be great to additionally consume a test container with a relational database through R2DBC by exposing the connection through a preconfigured ConnectionFactory.

ConnectionFactory is in R2DBC what a DataSource is in JDBC. R2DBC drivers are available for:

• PostgreSQL
• Microsoft SQL Server

More to come eventually.

Right now I can think of the following consumption scenarios:

• Pure JDBC (available today)
• JDBC and R2DBC (would make a lot of sense for testing as JDBC can help to prevent additional synchronization in cases where fixtures are prepared via JDBC and the actual application consumes data using reactive APIs)
• R2DBC-only (useful in pure reactive environments)

Inizia tracciando come i container di test per database relazionali espongono attualmente l'accesso JDBC, quindi confronta l'entry point ConnectionFactory di R2DBC SPI collegato nell'issue. Il lavoro è completato quando un container di test per database relazionali può essere utilizzato tramite una ConnectionFactory preconfigurata, mentre gli scenari JDBC esistenti e quelli combinati JDBC/R2DBC rimangono disponibili.