Handle refresh of cached files

[matildastevenson]

A user can do this themselves by just deleting the file, but then the actual files and the metadata.rds files will not be in sync. Some options are:

• Adding a function e.g. delete_cached_files
• Adding a third option to the caching config- something like ala_config(caching = "refresh").
• Another way would be to add refresh or update_cache as an optional argument to ala_ functions