Move time_zone setting outside of initializer

[thlacroix]

In the pghero initializer, we read the PgHero.config to check the time_zone. The default_config access some information via ActiveRecord::Base. This caused ActiveRecord::Base to be loaded too early (cf rails/rails#50133), and in this case we can simply avoid accessing it during initialization by just moving where we set the time_zone.

[ankane]

Hi @thlacroix, thanks for reporting and the PR. Pushed a minimal change in the commit above to address this.

[thlacroix]

Thanks for the fix !