Migration to plugin template and add climpact functionality

In this merge request, w migrated the plugin to the plugin template and added Climpact functionality with the specified configuration. Please check the README for instructions on plug and testing the plugin. Let me know if you face any issues. Also, we should schedule a meeting to discuss the next steps on the statistical methods together.

But still there is a big room for developing here. Files organization don't look good to me which we need to take care of that.

One production test is located here. So it mean every time you push into the repository, you test the plugin on production as I did in the following link. But no worries, in the meeting I explain it in detail

https://ch1187.gitlab-pages.dkrz.de/-/plugins4freva/heat2urbanimpact/-/jobs/505029/artifacts/build/prod_test/index.html

Closes #1 (closed)

wrapper.py

@@ -113,7 +113,7 @@ class Heat2UrbanImpact(plugin.PluginAbstract):
         SelectField(
             name="event",
             default="95",
-            options={"75th percentile": "75", "85th percentile": "85", "95th percentile": "95"},
+            options={"75": "75th percentile", "85": "85th percentile", "95": "95th percentile"},
             help="Select the exceptionality of the heat/warm period by selecting percentiles of temperature probability distribution. Default is the 95th percentile. IT'S NOT IMPLEMENTED YET.",
         ),
         Integer(