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>

runtime/src/snapshot_config.rs

@@ -15,11 +15,11 @@ pub struct SnapshotConfig {
     /// Generate a new incremental snapshot archive every this many slots
     pub incremental_snapshot_archive_interval_slots: Slot,
 
-    /// Where to store the latest packaged snapshot archives
-    pub snapshot_package_output_path: PathBuf,
+    /// Path to the directory where snapshot archives are stored
+    pub snapshot_archives_dir: PathBuf,
 
-    /// Where to place the bank snapshots for recent slots
-    pub snapshot_path: PathBuf,
+    /// Path to the directory where bank snapshots are stored
+    pub bank_snapshots_dir: PathBuf,
 
     /// The archive format to use for snapshots
     pub archive_format: ArchiveFormat,