Explicitely log a warning when the helper doesn't support cache

Some helpers do not support cache (it means that the cache database will not be updated from the results of the API call). The current behaviour is quiet, no log, when the worker supports cache self.use_cache=True.

All helpers should have a CacheMode, either with the code to update the cache database, or to log a warning This API helper did not update the cache database.

Example -> list_element_metadata.

• Normal mode: full exec, nothing happens
• Cache usage enabled (self.use_cache=True): full exec + warning message.