[12.x] Add createMany mass-assignment variants to HasOneOrMany relation

[onlime]

In Eloquent's HasOneOrMany relation, we have the following methods: create(), createQuietly(), forceCreate(), and forceCreateQuietly(). But to create a collection of new instances of the related model, we only have createMany() and createManyQuietly. I found myself searching for such mass-assignment variants over and over again.

In data import actions, I do this:

collect($comments)
    ->map(fn (array $comment) => [
        ...$comment,
        // override some attributes here
    ])
    ->each(fn (array $comment) => $post->comments()->forceCreateQuietly($comment));

With this PR, we can use use the lovely splat operator ... to pass all items directly into the forceCreateManyQuietly() method:

collect($comments)
    ->map(fn (array $comment) => [
        ...$comment,
        // override some attributes here
    ])
    ->pipe($post->comments()->forceCreateManyQuietly(...));

This PR adds the missing forceCreateMany() and forceCreateManyQuietly() methods.