Reinstate dependency management for org.mariadb:r2dbc-mariadb as it now supports R2DBC 1.0

[mshima]

spring-boot 2 supported mariadb-r2dbc though r2dbc-bom.
r2dbc-bom managed dependencies was integrated into spring-boot 3 at #31702, except mariadb which didn't support r2dbc 1.0 specs.

mariadb-r2dbc now supports r2dbc 1.0 https://github.com/mariadb-corporation/mariadb-connector-r2dbc/tree/1.1.3.
spring-data-relational added mariadb-r2dbc support at spring-projects/spring-data-relational#1364.

Would be nice if spring-boot adds mariadb-r2dbc to managed dependencies.