Make yiisoft/assets dependency optional

[vjik]

In project, bootstrap can be added in different ways and Yii Assets usage is one of them only. For example, user can get bootstrap by YARN and manually connect to project without Yii Assets usage. So we should make Yii Assets dependency optional.

[samdark]

True but that introduces some inconvenience i.e. "just composer install" won't work anymore, it will require some manual configuration.

[samdark]

@terabytesoftw what do you think?

[vjik]

True but that introduces some inconvenience i.e. "just composer install" won't work anymore, it will require some manual configuration.

It's already done: https://github.com/yiisoft/yii-bootstrap5?tab=readme-ov-file#install-assets