Add priority to register_middleware method

[ahopkins]

Closes #2596

[codecov]

Codecov Report

Base: 88.615% // Head: 88.640% // Increases project coverage by +0.025% 🎉

Coverage data is based on head (22f296d) compared to base (911485d).
Patch coverage: 100.000% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2636       +/-   ##
=============================================
+ Coverage   88.615%   88.640%   +0.025%     
=============================================
  Files           82        82               
  Lines         6746      6761       +15     
  Branches      1152      1156        +4     
=============================================
+ Hits          5978      5993       +15     
  Misses         529       529               
  Partials       239       239               

Impacted Files	Coverage Δ
sanic/app.py	90.070% <100.000%> (+0.234%)	⬆️
sanic/middleware.py	96.969% <100.000%> (+0.195%)	⬆️

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