Allow user to explicitly untrack file

[Archit404Error]

Currently, when a new ignored glob is added to config.json, only new files matching this glob are ignored and tracked files remain tracked (unless the user deletes and recreates the file). Give user the option to explicitly untrack a tracked file or folder to avoid this

[Archit404Error]

Ignored files are now deleted upon update (i.e., when user saves the file) and should be ignored from all indexing and reconciliation, but need to prevent them from being shown in search results.

In other words, previously indexed files that are now ignored still continue to exist in the DB.

One way to do this is to move the logic for skipping over ignored files out of the workspaceDFS method and into the respective callbacks for indexing and reconciling files. The indexing callback would skip over them and the reconciliation would delete them. However, this would only work if the user restarts vscode after marking a tracked files as ignored.

An alternative would be to run DFS and exclude newly matched files whenever reloadIgnoredFiles is called.

Need to think more about which approach to take