[Feature request] Configurable datetime format for naming output files

[jdvorak001]

Please check this repo whether this is a known feature request
I can’t see anything. This is also indirectly confirmed in a discussion with @drwetter in #2901.

Describe your feature request (if it's a technical feature)
I have the need for more or less granular or differently formatted datetimes in the names of output files produced by testssl.sh.

If your feature request otherwise is related to a usage problem, please describe it
I’d appreciate this flexibility for a larger-scale experiment where the resulting dataset should be shared.

Describe the solution you'd like
I’d like to have a command-line option and an environment variable through which the format for the date command could be specified.

Which version are you referring to
3.3dev

Do you volunteer to contribute a PR?
Yes.