Skip connection for datasources with omitted db configuration

[hertg]

This change will prevent issue #402 by skipping the creation and registration of a DatabaseConfig for ebean datasources which have no db connection parameters configured.

With this PR, users are able to specify and enhance Ebean models for datasources that may not be available on application startup, or that may be connected at a later stage during runtime. The ebean.<datasource> configuration can be specified without the need to also specify db.<datasource>.

play.evolutions.db.foo.enabled = false
ebean.foo = ["models.foo.*"]

// NOT CONFIGURED
// db.foo { 
// }

After a few tests, this seems to behave as I'd expect.

• Trying to query a model that was skipped will lead to the DataSource user is null? exception
• Once a connection is establised manually (see below), querying the model becomes possible

// manually connect the datasource
final DataSourceConfig dsc = new DataSourceConfig();
dsc.setUsername("username");
dsc.setPassword("password");
dsc.setUrl(connectionString("localhost", "my_schema");
final DatabaseConfig databaseConfig = new DatabaseConfig();
databaseConfig.setDataSourceConfig(dsc);
databaseConfig.setName("foo");
databaseConfig.setDefaultServer(false);
DatabaseFactory.create(databaseConfig);

---

I added a Logger to print information about the server config being skipped. I was not able to find a reference on how this should be done, so I did it the same way I'd do it in a Play application, by using play.Logger.ALogger. Let me know if this needs change.

[ihostage]

@Mergifyio backport 7.0.x

[mergify]

backport 7.0.x

✅ Backports have been created

• #405 [7.0.x] Skip connection for datasources with omitted db configuration (backport #403) by @hertg has been created for branch 7.0.x