Allow to define metadata when creating a new document

[matthenning]

In certain use cases we need to define _id when creating a new document.
The newInstance method already allows to pass $metadata as an optional second parameter.
By adding this optional parameter to the create method, we can allow the user to define _id as a metadata field.

Model::create([
  'name' => 'something',
], [
  '_id' => 'my-id-123'
]

[Radiergummi]

Hey @matthenning, thanks for opening this PR! I'm still thinking about whether making metadata part of the public API is the best solution to this problem: _id is the only metadata field that actually makes sense to be settable.
What do you think of the following:

Model::create([
    'name' => 'something',
], 'my-id-123');

[matthenning]

That's a valid concern, index and type are already covered via model properties anyway, so no need to expose them via the create method.
How about this version of the create method then?
Would that work for you? In that case I'll go ahead and update the PR.

/**
 * Save a new model and return the instance.
 *
 * @param array $attributes
 * @param string|null $id
 * @return static
 * @psalm-suppress LessSpecificReturnStatement
 */
public static function create(array $attributes, string $id = null): self
{
    $metadata = [];
    if (!is_null($id)) {
        $metadata['_id'] = $id;
    }

    return tap(
        (new static())->newInstance($attributes, $metadata),
        static function ($instance) {
            $instance->save();
        }
    );
}

[Radiergummi]

Looks fine, just make sure to make the ID parameter type a nullable string:

public static function create(array $attributes, ?string $id = null): self

[Radiergummi]

Thank you for contributing! 🎉