Maintenance mode with flags

[peterfox]

Changes In Code

• Added a Maintenance Mode driver
• Adds tests for this
• Adds an extension of the PreventRequestsDuringMaintenance to allow the use of the except value otherwise, this won't work.

Issue ticket number / Business Case

Maintenance Mode within the package will allow for more complex configurations where the feature flags decide the state of maintenance mode and how the application should handle things in the event of a problem.

Example code:

Features::maintenanceMode()
            ->onEnabled('system.api')
            ->statusCode(500);

Checklist before requesting a review

• I have written PHP tests.
• I have updated the documentation in the readme where needed.
• I have checked code styles, PHPStan etc. pass.
• I have provided an issue/business case.

[codecov-commenter]

Codecov Report

Merging #54 (1622945) into main (c9869c6) will increase coverage by 2.77%.
The diff coverage is 94.73%.

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@@             Coverage Diff              @@
##               main      #54      +/-   ##
============================================
+ Coverage     80.26%   83.03%   +2.77%     
- Complexity      170      201      +31     
============================================
  Files            27       31       +4     
  Lines           461      554      +93     
============================================
+ Hits            370      460      +90     
- Misses           91       94       +3     

Impacted Files	Coverage Δ
src/Facades/Features.php	100.00% <ø> (ø)
src/Support/MaintenanceRepository.php	85.71% <85.71%> (ø)
src/FeatureFlagsServiceProvider.php	98.55% <100.00%> (+0.33%)	⬆️
src/Manager.php	60.38% <100.00%> (+0.52%)	⬆️
...c/Middlewares/PreventRequestsDuringMaintenance.php	100.00% <100.00%> (ø)
src/Support/MaintenanceDriver.php	100.00% <100.00%> (ø)
src/Support/MaintenanceScenario.php	100.00% <100.00%> (ø)
src/Support/FeatureFake.php	100.00% <0.00%> (+8.00%)	⬆️

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