[FEAT] Add WatchFileSystem Activity

[adamfisher]

Feature Request

Problem Overview

A common scenario workflow users come across is waiting for a file or folder in a directory to be created or changed before taking action.

Proposed Solution

The solution would be to add a new activity that integrates the .NET FileSystemWatcher into a new WatchFileSystem activity that allows a workflow user to specify a path segment to watch which suspends the workflow until the watch conditions are satisfied, at which point the workflow is resumed.

Activity Inputs:

• Path: The path to the directory to watch for changes.
• File Filter: The filter string, used to determine what files are monitored in a directory. Supports a simplified set of regular expressions.
• Event Type: Dropdown selection of Changed, Created, Deleted, Renamed
• Notification Types: A dropdown selection of the type of changes to watch for. These values will come from the NotifyFilters enum. (Can this be a multi-select? Would it make sense?)
• IncludeSubdirectories: Checkbox indicating whether subdirectories within the specified path should be monitored.
• Ignore Hidden Files: Checkbox indicating whether hidden files within the specified path should be monitored.
• Ignore Hidden Folders: Checkbox indicating whether hidden folders within the specified path should be monitored.

Activity Outputs:

• Directory: The Directory reference of the Path being watched.
• File: The File reference matching the watch conditions.

Use Cases

• Daily xml/json/csv/data files get dumped into a directory and I want to process them with Elsa when they become available.
• I need to wait for a file exist before a downstream activity or workflow can begin execution and this WatchFileSystem activity would provide suspension capability until the file exists.

[sfmskywalker]

Makes sense. We have this in Elsa 2, might be portable to Elsa 3 or at least serve as an inspiration.