[9.x] Add read-only filesystem adapter decoration as a config option

[frankdejonge]

This PR adds the ability to configure a disk to operate in read-only mode. When this option is set to true, the underlying adapter is decorated with an implementation that ensures no write operation is possible on the disk. This is useful when you're receiving files through a shared storage, but you shouldn't manipulate any of the files stored.

If interested, I can also add a PR to include a path prefixing decorator: https://flysystem.thephpleague.com/docs/adapter/path-prefixing/

[taylorotwell]

@frankdejonge is there any need for us to pass any of these options like temporary_url?

[driesvints]

@taylorotwell those options are still passed as the new adapter is just a decorator.

[taylorotwell]

Ah, sorry - read the code wrong.