backups: add setup/teardown

1. add setup, teardown hooks
2. move the managed mount setup and teardown to filesystem backend
3. remove this vague storage.js

we should convert storageApi into a real object, so we don't have to
keep passing apiConfig around

src/backupformat/tgz.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const assert = require('assert'),
+    backupTargets = require('../backuptargets.js'),
     BoxError = require('../boxerror.js'),
     DataLayout = require('../datalayout.js'),
     debug = require('debug')('box:backupformat/tgz'),
@@ -10,7 +11,6 @@ const assert = require('assert'),
     ProgressStream = require('../progress-stream.js'),
     promiseRetry = require('../promise-retry.js'),
     safe = require('safetydance'),
-    storage = require('../storage.js'),
     stream = require('stream/promises'),
     { Transform } = require('node:stream'),
     tar = require('tar-stream'),
@@ -244,7 +244,7 @@ async function download(backupTarget, remotePath, dataLayout, progressCallback)
     await promiseRetry({ times: 5, interval: 20000, debug }, async () => {
         progressCallback({ message: `Downloading backup ${backupFilePath}` });
 
-        const sourceStream = await storage.api(backupTarget.provider).download(backupTarget.config, backupFilePath);
+        const sourceStream = await backupTargets.storageApi(backupTarget).download(backupTarget.config, backupFilePath);
         await tarExtract(sourceStream, dataLayout, backupTarget.encryption, progressCallback);
     });
 }
@@ -262,7 +262,7 @@ async function upload(backupTarget, remotePath, dataLayout, progressCallback) {
     await promiseRetry({ times: 5, interval: 20000, debug }, async () => {
         progressCallback({ message: `Uploading backup ${backupFilePath}` });
 
-        const uploader = await storage.api(backupTarget.provider).upload(backupTarget.config, backupFilePath);
+        const uploader = await backupTargets.storageApi(backupTarget).upload(backupTarget.config, backupFilePath);
         await tarPack(dataLayout, backupTarget.encryption, uploader, progressCallback);
     });
 }