This commit adds warnings, if the exported asset's size does not match the expected size.
The result made me curious, as one of the assets from the `backup.zip` test reports a warning when testing with `backupEnvironment` (the size of the `.jpg`: expected 27_093 bytes, got 27_002 bytes).
Even though, this commit adds a warning for individual assets, and reports a warning count as the result of the operatoin ("Entities from environment <ENV_ID> were backd up with X warning(s) into ...).
This commit takes the liberty to rephrase "backuped" -> "backed up".

```
Exporting entities from environment id <ENVIRONMENT_ID>

Exporting: collections
[...]
Exporting: assetFolders
Exporting: assets
Exporting: file kontent-app.webp.
Exporting: file kontent-calendar.png.
Exporting: file kontent-logo-2.avif.
Exporting: file kontent-ai.png.
Exporting: file kai-hp-highlight-3.jpg.
Size mismatch: expected 27093 bytes, got 27002 bytes.
Exporting: file kai-logo-ver-black-rgb.svg.
Exporting: file kai-logo-ver-neg-rgb.svg.
Exporting: webhooks
Exporting: webSpotlight

Entities from environment <ENVIRONMENT_ID> were backd up with 1 warning(s) into 2024-11-24-10-55-backup-<ENVIRONMENT_ID>.zip.
```

Partially fixes kontent-ai#100

This reverts commit 2f880a6.

…cureAssetDeliveryKey`

Fixes kontent-ai#100