Check file existence in localstore
Current situation
Currently, some ExecutionResult events may contain attachments that do not exist as file. The localstore service does not check for the file existence before adding its path to the workflow attachments list: later, when it tries to delete a non-existent file, warning messages are generated.
Desired outcome
The localstore service must check file existence before mapping an attachment to the workflow. Besides, it would be interesting to create a new user-faced endpoint for the file existence check, allowing, on the tools side, to verify if the attachment exists as file without downloading it.