feat: allow passing custom axios instance to createInertiaApp

[LeTamanoir]

No description provided.

[reinink]

What's the purpose of this change?

[wfern]

@reinink he explains it in detail in the issue: #2103

[pascalbaljet]

I get the problem, but changing this would be a breaking change, as I know that people are relying on the global Axios instance, for example, to set additional headers to send with each request.

If you can refactor it to something that you can pass as an option/resolver into createInertiaApp(), then I'm fine with it.

[LeTamanoir]

Hey @pascalbaljet sorry I missed your reply, I'll update my PR with your suggestions 👍

[LeTamanoir]

Hey @pascalbaljet I updated the PR.
I went with a static property as it seemed to need less code to change.
Not sure if it fits the code style of the project though 🫤 what do you think ?