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

@@ -83,7 +83,7 @@ class BaseTableExporter(object):
             ```
             {"entry_to_be_exported: {
                 "optional": True/False
-                "find_func": name of member function
+                "find_func": callable or name of member function
                 "query": query string
                 "selector": selector for the query
                 "error": error explanation
@@ -97,8 +97,8 @@ class BaseTableExporter(object):
             - optional: True or False, if not present, the entry is
               assumed to be mandatory.
             - find_func: name of the member function that returns the
-              value for this entry. Must not exist together with
-              `query`
+              value for this entry or callable object. Must not exist
+              together with `query`
             - query: Query string for finding the value for this
               entry. If this is given, a record must be given to the
               constructor of this class. The query is then executed as
@@ -163,7 +163,10 @@ class BaseTableExporter(object):
                 else:
                     self._append_missing(e, d)
             elif FIND_FUNCTION in d:
-                find_fun = getattr(self, d[FIND_FUNCTION])
+                if callable(d[FIND_FUNCTION]):
+                    find_fun = d[FIND_FUNCTION]
+                else
+                    find_fun = getattr(self, d[FIND_FUNCTION])
                 try:
                     self.info[e] = find_fun()
                 except Exception as exc:
@@ -287,7 +290,9 @@ class BaseTableExporter(object):
             # check find function if present
 
             if FIND_FUNCTION in d:
-                if not hasattr(self, d[FIND_FUNCTION]):
+                if callable(d[FIND_FUNCTION]):
+                    pass
+                elif not hasattr(self, d[FIND_FUNCTION]):
                     raise TableExportError(
                         "Find function " + d[FIND_FUNCTION] +
                         " was specified for entry " + e +