Update all code snippets in docs to use Bootstrap 5

[greyli]

For example, at the macros.rst page (https://bootstrap-flask.readthedocs.io/en/stable/macros/), replace all import statements from

{% from 'bootstrap4/nav.html' import ... %}

To:

{% from 'bootstrap5/nav.html' import ... %}

[AbhishekMaurya2002]

Hi, i know how to do it,can you please assign to me?

[greyli]

Sure, no problem.

[MysteryManav]

I would like to work on this issue, but i have a doubt, in the entire docs, only the import statements are to be changed to bootstrap5 ? or do you want the Bootstrap() class initialization examples to also be changed to Bootstrap5. Also mention if there are any other changes to be done

[greyli]

AFAIK, only the import statements and extension class initialization need to be updated.