Add support for nested tenant config override

[rootgog]

This PR adds the ability to assign from nested JSON values on the Tenant model while staying backwards compatible with the existing implementation.

Essentially eloquent's model getAttribute is replaced with the Laravel helper function Arr::get when the values are extracted from the tenent model which allows for dot notated paths to be used to map nested JSON values.

For example this allows implementations such as the following

\Stancl\Tenancy\Features\TenantConfig::$storageToConfigMap = [
    'whitelabel.config.theme' => 'whitelabel.theme',
];

[stancl]

Hey, thanks for the PR! I was trying to find a past discussion about this because I think there was a convo about how this part of the code works, so I wanted to check if there'd be any problem with using Arr::get(). But it seems like this will work fine.

I found this issue #412 and that may have been it (I think there was some other discussion too but this looks similar enough). Essentially, "supporting arrays" is a thing on both sides of the foo => bar mapping here. I believe the commit which fixed #412 6dad6ce added support for mapping a single tenant value to multiple config values.

And this PR will support reading from arrays on the tenant side. Is that correct?

The implementation looks good and so does the test. Though I think I'll change the target to 4.x. We're focusing on v4 development now so we prefer that new features are added there, and 3.x changes are only things like urgent bug fixes.

If I change the target branch, there will likely be a conflict in the test file, since we migrated to pest on the master branch. You can try resolving that on your own, or @abrardev99 will fix it on Monday and we'll get this merged 👍🏻

[stancl]

Ah hmm, seems like your branch is based on 3.x which has some additional changes that can't be easily merged. I guess we'll merge this into 3.x then and merge 3.x into master

[stancl]

Thanks a lot for the PR!