bounded queue: block the hot thread instead of dropping messages

[odygrd]

Discussed in #269

^{Originally posted by brendene March 14, 2023}
Hello and thanks again for the library! Would you consider a logging mode where log messages are not dropped and the queue is non allocating? i.e. blocking

A use case would be stress testing a webserver that uses quill for logging. When the webserver is running in real time, logs are flushed to disk and the queue isn't growing. However, if you are stress testing the webserver with a preset load and piping the output to less eventually the pipe buffer fills up and the quill backend thread isn't able to drain so the queue gets larger and larger until the system possibly runs out of memory.

I realize this isn't in the spirit of a low latency logger but it would be nice to be able to utilize the same logging code (perhaps with a config option that enables/disables it) without adding quill::flush() everywhere.