Add data-r2dbc README

Add lifecycle documentation.

data/data-r2dbc/README.adoc

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+Document lifecycle requirements with Spring Data R2DBC.
+
+== Lifecycle configuration guidance
+
+Spring Data R2DBC requires extra configuration to avoid early database interaction.
+
+```
+# Database initialization should typically be performed outside of Spring lifecycle
+spring.sql.init.mode=never
+```