Make the rails:template rake task load initializers

Templates could rely on irregular inflections or external libraries for
instance so we should load the application's initializers when running
the rails:template task.

The introducing commit of this feature is f7f11361 ; the initializers
have never been loaded invoking this task.

Fixes #12133.
Merge pull request #14325 from robin850/issue-12133

Make the rails:template rake task load initializers