RFE: new parameter for perflog file name

[flx42]

This is a follow-up of https://github.com/reframe-hpc/reframe/issues/2577 and the comment https://github.com/reframe-hpc/reframe/pull/2578#issuecomment-1231358999

The request is to have a way to control the filename of the filelog output file, in order to have a human-readable filename like ib_write_bw_loopback_mlx5_6.log (where mlx5_6 is a test parameter) when listing files, instead of having ib_write_bw_loopback_<hash>.log

In addition to having a way to control the filename, I suppose we also need a way in the ReFrame settings file to stringify the test parameters in order to get a filename similar to what we had in ReFrame 3.x.

Thanks!