Enhance status with reporting maximum number of open files (sockets)

[michaelortmann]

Found by: michaelortmann Patch by: michaelortmann Fixes:

One-line summary:

Additional description (if needed): While working on dns async code with threads and pipes it came to me, that enhancing .status with reporting maximum number of open files (sockets) could be useful. but i wanted the dns PR to be slim, so i copid the work for .status over to this new PR.

Test cases demonstrating functionality (if applicable):

.status
[...]
Maximum number of open files (sockets): soft limit 1024 hard limit 524288