Add hint for new dependencies required for Flyway

See gh-41574

Author: jmewes

spring-boot-project/spring-boot-docs/src/docs/antora/modules/how-to/pages/data-initialization.adoc

@@ -98,6 +98,7 @@ Spring Boot supports two higher-level migration tools: https://flywaydb.org/[Fly
 === Execute Flyway Database Migrations on Startup
 
 To automatically run Flyway database migrations on startup, add the `org.flywaydb:flyway-core` to your classpath.
+All databases that are not in-memory or file based need an additional dependency, e.g. `org.flywaydb:flyway-database-postgresql` is required for PostgreSQL and `org.flywaydb:flyway-mysql` is required for MySQL (see https://documentation.red-gate.com/flyway/flyway-cli-and-api/supported-databases[Supported Databases in the Flyway Documentation] for details).
 
 Typically, migrations are scripts in the form `V<VERSION>__<NAME>.sql` (with `<VERSION>` an underscore-separated version, such as '`1`' or '`2_1`').
 By default, they are in a directory called `classpath:db/migration`, but you can modify that location by setting `spring.flyway.locations`.