This diff introduces the addition of the `init` and a global configuration struct to use in sending notifications functions to avoid duplication of providing the same parameters in the functions.
Instead of providing a certificate, fcm key for every function call we can initialize it once the service starts.
The usage changes are introduced in the next D5330.
Related Linear task: [[ https://linear.app/comm/issue/ENG-1737/change-to-use-builder-approach-and-thread-local-in-rust-notification | ENG-1737 ]]