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>

ledger-tool/src/main.rs

@@ -699,7 +699,7 @@ fn load_bank_forks(
     process_options: ProcessOptions,
     snapshot_archive_path: Option<PathBuf>,
 ) -> bank_forks_utils::LoadResult {
-    let snapshot_path = blockstore
+    let bank_snapshots_dir = blockstore
         .ledger_path()
         .join(if blockstore.is_primary_access() {
             "snapshot"
@@ -709,13 +709,13 @@ fn load_bank_forks(
     let snapshot_config = if arg_matches.is_present("no_snapshot") {
         None
     } else {
-        let snapshot_package_output_path =
+        let snapshot_archives_dir =
             snapshot_archive_path.unwrap_or_else(|| blockstore.ledger_path().to_path_buf());
         Some(SnapshotConfig {
             full_snapshot_archive_interval_slots: 0, // Value doesn't matter
             incremental_snapshot_archive_interval_slots: Slot::MAX,
-            snapshot_package_output_path,
-            snapshot_path,
+            snapshot_archives_dir,
+            bank_snapshots_dir,
             archive_format: ArchiveFormat::TarBzip2,
             snapshot_version: SnapshotVersion::default(),
             maximum_snapshots_to_retain: DEFAULT_MAX_FULL_SNAPSHOT_ARCHIVES_TO_RETAIN,