Calrifying risks of using truncate

[vadimonus]

This PR is some way opposite to #10116

The current documentation does not accurately describe the risks of using truncate (appeared in #6560).
Even it documentated for 4 years, users do not understand risks. See laravel/framework#35157 (comment) and later in thread.

This PR clarifies potential problems, that comes with truncate

• recursive data deletion for postgresql (not only foreign key related records, but all records)
• data inconsistency for mysql

[shaedrich]

As mentioned in #10116, I think, putting a warning into the docs is the better solution as long as this functionality exists in the framework. Thanks for creating this PR therefor 👍🏻

[taylorotwell]

No plans to add this right now.