Output png file naming according to ProductBrowser requirements

[pirmink]

Output file naming is currently always according to NAZ requirements.

This is correct for the pdf files, which are sent to the NAZ:
<start-date/-time (iso8601): yyyymmddThh>_<site-name>_LAGRANTO-<nwp-model-name (without -EPS)>-CTRL_Trajektorien_<direction: F | B>_<duration: hhh>_<plot-domain>.<image-format>

Example:
20260122T06_Beznau_LAGRANTO-ICON-CH1-CTRL_Trajektorien_F_042_alps.pdf

The same naming is currently also used for png files, which are meant to be sent to the ProductBrowser.

Example:
20260122T06_Beznau_LAGRANTO-ICON-CH1-CTRL_Trajektorien_F_042_alps.png

The ProductBrowser however cannot interpret these filenames. Instead of renaming them with a script, they should be produced directly by pytrajplot with names according to the ProductBrowser requirements:
forecast-<nwp-model-shortname>-trajectories~<nwp-model-base-date/-time (iso8601): yyyymmddThh>~<direction: forward | backward>~<plot-domain>~<site-name>~<start-date/-time (iso8601): yyyymmddThh>.png

Example:
forecast-iconch1eps-trajectories~20260122T03~forward~alps~Beznau~20260122T06.png