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/accounts_hash_verifier.rs

@@ -293,8 +293,8 @@ mod tests {
         let snapshot_config = SnapshotConfig {
             full_snapshot_archive_interval_slots,
             incremental_snapshot_archive_interval_slots: Slot::MAX,
-            snapshot_package_output_path: PathBuf::default(),
-            snapshot_path: PathBuf::default(),
+            snapshot_archives_dir: PathBuf::default(),
+            bank_snapshots_dir: PathBuf::default(),
             archive_format: ArchiveFormat::Tar,
             snapshot_version: SnapshotVersion::default(),
             maximum_snapshots_to_retain: usize::MAX,