Name snapshots consistently (#19346)

#### Problem

Snapshot names are overloaded, and there are multiple terms that mean the same thing. This is confusing. Here's a list of ones in the codebase that I've found:

```
- snapshot_dir
- snapshots_dir
- snapshot_path
- snapshot_output_dir
- snapshot_package_output_path
- snapshot_archives_dir
```

#### Summary of Changes

For all the ones that are about the directory where snapshot archives are stored, ensure they are `snapshot_archives_dir`. For the ones about the (bank) snapshots directory, set to `bank_snapshots_dir`.


Co-authored-by: Michael Vines <mvines@gmail.com>

core/src/snapshot_packager_service.rs

@@ -121,8 +121,8 @@ mod tests {
     fn create_and_verify_snapshot(temp_dir: &Path) {
         let accounts_dir = temp_dir.join("accounts");
         let snapshots_dir = temp_dir.join("snapshots");
-        let snapshot_package_output_path = temp_dir.join("snapshots_output");
-        fs::create_dir_all(&snapshot_package_output_path).unwrap();
+        let snapshot_archives_dir = temp_dir.join("snapshots_output");
+        fs::create_dir_all(&snapshot_archives_dir).unwrap();
 
         fs::create_dir_all(&accounts_dir).unwrap();
         // Create some storage entries
@@ -161,7 +161,7 @@ mod tests {
 
         // Create a packageable snapshot
         let output_tar_path = snapshot_utils::build_full_snapshot_archive_path(
-            snapshot_package_output_path,
+            snapshot_archives_dir,
             42,
             &Hash::default(),
             ArchiveFormat::TarBzip2,