ENG-6216 : Add rust code for getting filepath with compations/logs
Adds two new functions for files used for backup data storage on the device (while they are waiting to be confirmed by backup service): one for logs (with optional attachments file) and the second one for userkeys file.

Additionally changes the functions to take &str (rust::Str) instead of String (rust::String) as we are making a copy of them to std::string immediately and don't need to pass an owned string.

Depends on D10604

Called these functions from rust and got these results:

backup-123-userkeys
backup-123-log-456
backup-123-log-456-attachments