replace the usage of GORM in Guides

[sdelamo]

GORM does not support Groovy 4. yet. Thus, Micronaut Framework 4.0 does not support GORM yet. We have two guides which use GORM.

• [x] micronaut-database-authentication-provider
• [ ] micronaut-multitenancy-propagation

We should replace GORM for something like Micronaut Data JDBC.

[sdelamo]

I have rewritten micronaut-database-authentication-providerto use Micronaut Data JDBC instead.