Allow draft files to be shared

[vinstah]

Description

Adding Extension to Assets to allow the ability to share them.

Additional context or points of discussion

A website user uploads a file that is a secured asset, and gets a confirmation email with a link to that asset but cannot view it as they don't adhere to the secured assets permissions on ProtectedAssetsController (this could be a check in FlysystemAssetStore)
sending the email with a preview link helps instead

Validations

• You intend to implement the feature yourself
• You have read the contributing guide
• You strongly believe this feature should be in core, rather than being its own community module
• You have checked for existing issues or pull requests related to this feature (and didn't find any)