More flexible naming of the output files

[mandresm]

As agreed during a meeting on 25.06.2021 with @koldunovn , it would be great if PyFesom could support a wider range of naming conventions for FESOM output files.

At the moment it only supports the following naming convention:

<variable>.<ID>.<Year>.nc

However, in ESM-Tools for example, we often do monthly and even daily restarts, and copy these files into a common folder, therefore needing to change the name using a time stamp. The format we've been using for that is:

<cariable>.<ID>.<YearMonth>.<Day>.nc

An example of how the output looks like for a finished simulation of AWICM3 using ESM-Tools can be found here: /work/ollie/mandresm/esm_yaml_test/eternal_awicm3_daily/outdata/fesom/

[pgierz]

Can I give double thumbs up? This has driven me crazy. We also could allow a switch on the esm-tools side