Add support for BackPack v6

[jnoordsij]

Encountered while testing out the new v6 beta. Currently no version (including the 6.x-dev version) supports the new v6 beta. It would be nice to have a v6-compatible version for testing this when running the beta, to ensure everything works fine ;)

[tabacitu]

Just pushed a fix to #26 so that you can use that branch in v6. So you should be able to do composer require backpack/filemanager:"v6.x-dev" and get the branch with v6 support.

[de-raaf-media]

Hi @tabacitu, is the filemanager not ready for production yet? I installed the 6.x-dev version and now get an error:

No hint path defined for [backpack].

This was all working. Just upgraded to Laravel 10 and Backpack 6.

[de-raaf-media]

And of course moments later I got it to work. I decided to compare the blade views. The filemanager install command does not override existing views apparently. Deleting the views and then execute filemanager installation works fine. So problem solved. Just an issue where the sidebar menu item is not added.

[tabacitu]

Hmmm right, I've just added an Upgrade section to the README. Thanks @de-raaf-media

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