Fix: use to_prepare to reset SMS config

related !625 (merged)

What does this MR do and why?

It's recommended to use Rails.application.config.to_prepare to reload constants or reset settings on boot and on each reload according to Rails Guides of version 7.0.3.

For Rails 6.1.3 we can use Rails.application.reloader.to_prepare from the guides of v6.1.0 since we are using 6.1.4.7 specified in Gemfile. We also have examples in GitLab about this usage, such as /config/initializers/lograge.rb#L5

• Revert the changes from !625 (merged)
• Use Rails.application.reloader.to_prepare to set SMS config after reloading

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