feat: Add {CLIENT_HOSTNAME} placeholder support for backup file patterns

[ryan-steed-usa]

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Brief Summary

Thanks for this excellent project. I use it with multiple clients (laptops, desktop, phone) to share a single database and the placeholder feature is very useful. But it could be improved for deployment with remote/synchronized storage.

I've submitted #12701 to add this capability. While related to #11105, this implementation employs Qt's QHostInfo::localHostName() function rather than an environment variable.

Example

It can allow for more generic keepassxc.ini configuration like:

[General]
BackupBeforeSave=true
BackupFilePathPattern={DB_FILENAME}-{CLIENT_HOSTNAME}.old.kdbx

Context

This especially benefits multi-client usage with synchronized or remote storage, like Nextcloud.