[Backups] Fix database dump error reporting

[Akkadius]

What

This PR fixes an issue where database dumps would not bubble stderr from the underlying process execution. Currently this pipes stderr to stdout so we don't miss errors, this could be later improved to hold a response object containing status stderr and stdout

This is to prevent server operators from experiencing any sort of data loss if they are missing a table that the database backup is trying to request explicitly. If a table is missing, mysqldump will normally stop.

We could ignore this but this really is something that should be addressed immediately otherwise it could cause worse pain to ignore.

• We now cleanup SQL files after compression is requested and a compression binary is found
• When a mysqldump error is detected, the world process is exited forcefully
• Added file utility File::GetContents(file_name)