feat(#72): implement static route

[francescovallone]

Description

Add the possibility to define static routes to return instantly something.

Fixes #72

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.78%. Comparing base (4e4f415) to head (73fd5a7).

Files with missing lines	Patch %	Lines
packages/serinus/lib/src/core/controller.dart	75.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #94      +/-   ##
===========================================
+ Coverage    90.74%   90.78%   +0.03%     
===========================================
  Files           77       77              
  Lines         2778     2810      +32     
===========================================
+ Hits          2521     2551      +30     
- Misses         257      259       +2     

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