[BUG] `cacache` caches don't contain `CACHEDIR.TAG`

[akx]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

cacache caches (e.g. those created by npm) don't contain a CACHEDIR.TAG file.

These files are useful markers that e.g. GNU tar supports to exclude archiving/backing up/... recreatable data.

Expected Behavior

cacache caches (or at least npm caches) should contain a CACHEDIR.TAG file.

Steps To Reproduce

1. In any environment
2. Cache something with cacache
3. See no CACHEDIR.TAG file in the cache

Environment

• npm: Any
• Node: Any
• OS: Any
• platform: Any