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/validator.rs

@@ -1210,7 +1210,7 @@ fn new_banks_from_ledger(
             ledger_path,
             &bank_forks.root_bank(),
             None,
-            &snapshot_config.snapshot_package_output_path,
+            &snapshot_config.snapshot_archives_dir,
             snapshot_config.archive_format,
             Some(bank_forks.root_bank().get_thread_pool()),
             snapshot_config.maximum_snapshots_to_retain,