merge database migration plugin into gorm-hibernate5 repository

[jamesfredley]

https://github.com/grails/grails-database-migration

grails-database-migration is dependent upon liquibase-core and liquibase-hibernate5. Given the dependency on liquibase-hibernate5 the historical version of grails-database-migration is being merged into the gorm-hibernate5 project, since they are tied at the hip by hibernate5. The current release of https://mvnrepository.com/artifact/org.liquibase.ext/liquibase-hibernate5/4.27.0 may be the last hibernate5 Liquibase release given the Apr 03, 2024 release date.

For this merge the maven coordinates will stay org.grails.plugins:database-migration, but the version will jump from 6.0.x to 9.0.x to match GORM and make it easier to confirm compatibility.

When gorm-hibernate6 is ready, a distinct version of database-migration should be merged into that project which supports hibernate6. It should have a distinct artifactid, such as database-migration-hibernate6.