PHPORM-264: Deprecate Mongo soft deletes trait

[paulinevos]

In favor of the Laravel one. Ours is now obsolete; the SoftDeletes trait is only necessary to remove the call to qualifyColumn in the parent trait. But the DocumentModel::qualifyColumn is already disabled.

Also replaces some internal/test usages with the recommended trait.

Closes PHPORM-264

Checklist

• Ensure tests still pass

[rustagir]

changes to docs tests lgtm

[paulinevos]

Sorry this took me so long @GromNaN. Question, why do we trigger an error instead of a deprecation here?

[GromNaN]

Question, why do we trigger an error instead of a deprecation here?

trigger_deprecation is a Symfony function to call trigger_error with the E_USER_DEPRECATED level. "deprecated" is just one level among others such as "error" and "warning". I don't know of any other way to do it.

[paulinevos]

Gotcha, thank you!