Adds middleware to enforce 2fa

[singh1114]

Description

As far as I know, The current 2FA enforcement involves admin intervention. With the following change, people can directly include middleware in the settings file and things will work out of the box.

Motivation and Context

We are using this software for in our django app. We wanted to enforce 2FA. But the existing solution doesn't allowed the free movement and stopped the user from moving forward if the user has not enabled 2FA.

We wanted it differently, we wanted the users to move forward but only to the urls where the user can either logout or enable 2FA.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[singh1114]

@Bouke Please check if the following change is required or not. If yes, Please share if you want any modifications as well.

[codecov[bot]]

Codecov Report

Merging #284 into master will decrease coverage by 0.68%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
- Coverage   96.52%   95.84%   -0.69%     
==========================================
  Files          39       40       +1     
  Lines        1640     1660      +20     
  Branches      116      118       +2     
==========================================
+ Hits         1583     1591       +8     
- Misses         35       47      +12     
  Partials       22       22

Impacted Files	Coverage Δ
two_factor/middleware/enforce2fa.py	0% <0%> (ø)
tests/test_utils.py	100% <0%> (ø)	:arrow_up:

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