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/test_validator.rs

@@ -523,8 +523,8 @@ impl TestValidator {
             snapshot_config: Some(SnapshotConfig {
                 full_snapshot_archive_interval_slots: 100,
                 incremental_snapshot_archive_interval_slots: Slot::MAX,
-                snapshot_path: ledger_path.join("snapshot"),
-                snapshot_package_output_path: ledger_path.to_path_buf(),
+                bank_snapshots_dir: ledger_path.join("snapshot"),
+                snapshot_archives_dir: ledger_path.to_path_buf(),
                 archive_format: ArchiveFormat::Tar,
                 snapshot_version: SnapshotVersion::default(),
                 maximum_snapshots_to_retain: DEFAULT_MAX_FULL_SNAPSHOT_ARCHIVES_TO_RETAIN,