fix: use app documents directory to store the user token if possible

[VladislavFitz]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Related Issue	Fix #84
Need Doc update	no

Describe your change

This pull request introduces the utilization of the path_provider package to enable access to the application documents directory on iOS, Android, macOS, Linux, and Windows platforms. By incorporating this package, we can ensure a consistent and secure storage location for user tokens.

What problem is this fixing?

Unhandled FileSystem exceptions on some platforms (iOS) while trying to store the persistent user token

[aallam]

Nice Job!

[aallam]

This is perfect! Nice job!
By the way, if in the future isWeb is used in more than one place, we could refactor the import logic into another file. However, for now, it's good as it is. :)

[nerder]

What's preventing this PR from being merged? Also, I think it should close mine as soon as this is merged as it aims to fix the same issue.

[VladislavFitz]

@nerder it's blocked because path_provider library requires Flutter as dependency while Insights is a pure Dart library. We are still deciding how to proceed, most likely the Insights library will become the Flutter library. The release will be soon.