remove: add retries to client directory removal

Summary:
While debugging `sl worktree add` failures, one failure came across as a failed eden removal -> corrupt eden state ->  failed worktree add. The user seemed to have ran `eden doctor` which got them to a better state, but I'd like to try to address the root issue.

Their eden removal failed with (https://fburl.com/scuba/edenfs_cli_usage/ogclkwez) :

```
Failed to remove client config directory for {removal_target}: Directory not empty (os error 39)
```

as per: https://doc.rust-lang.org/std/fs/fn.remove_dir_all.html#errors

> This function may return `io::ErrorKind::DirectoryNotEmpty` if the directory is concurrently written into, which typically indicates some contents were removed but not all. `io::ErrorKind::NotFound` is only returned if no removal occurs.

On the host I investigated, there was only a `local` directory there, which was half removed. So there must have been some outstanding overlay writes happening while the repo was being removed: P2265496617

This diff migrates to a retrying removal (used already in this file elsewhere), which gives us a better chance of a removal if there are racing writes.

As a followup too, we probably want to treat this as non-fatal and continue removal. I suspect we will see more instances of removals happening with other processes using the repo, so these best effort retries might not be enough. I think its fair to honor the removal over the potential usage of a repo.

Reviewed By: janezhang10

Differential Revision: D99915460

fbshipit-source-id: b27b20725a7335ae0ec3eb50721e2395612bc0a7

Author: genevievehelsel

eden/fs/cli_rs/edenfs-commands/src/remove/utils.rs

@@ -25,8 +25,9 @@ use crate::get_edenfs_instance;
 
 pub fn remove_client_config_dir(context: &RemoveContext) -> Result<()> {
     let instance = get_edenfs_instance();
+    let client_dir = instance.client_dir_for_mount_point(&context.canonical_path)?;
 
-    match fs::remove_dir_all(instance.client_dir_for_mount_point(&context.canonical_path)?) {
+    match forcefully_remove_dir_all(&client_dir) {
         Ok(_) => Ok(()),
         Err(e) if e.kind() == ErrorKind::NotFound => Ok(()),
         Err(e) => Err(anyhow!(