ENH: more useful table export find func

Summary

1. Add support for passing callable to BaseTableExporter(find_func=callable)
2. Add BaseTableExporter.all_keys.

• Needed for https://git.geomar.de/dm/bis/indiscale/sample-management/-/merge_requests/8

Focus

The magic happens in BaseTableExporter._call_find_function.

Test Environment

Test with geomar setup

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src/caosadvancedtools/table_export.py

@@ -166,11 +166,15 @@ class BaseTableExporter(object):
                 else:
                     self._append_missing(e, d)
             elif FIND_FUNCTION in d:
-                val = self._call_find_function(d[FIND_FUNCTION], e);
-                if val is not None:
-                    self.info[e] = val
-                else:
+                try:
+                    val = self._call_find_function(d[FIND_FUNCTION], e)
+                    if val is not None:
+                        self.info[e] = val
+                    else:
+                        self._append_missing(e, d)
+                except Exception as exc:
                     self._append_missing(e, d)
+                    logger.error(exc)
             # last resort: check if record has e as property:
             else:
                 try: