feat: introduce new flag 'noAdditionalProperties' to add 'additionalProperties: false' to the generated JSON schema

[hajowieland]

Implements #38

• Introduces a new command-line flag noAdditionalProperties
• Extended the Config for the new flag
• Extended the Schema for additionalProperties to be added to all nodes
• Update Usage section in README

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (361856d) 98.58% compared to head (7dcc68b) 97.90%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
pkg/parser.go	66.67%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   98.58%   97.90%   -0.68%     
==========================================
  Files           6        6              
  Lines         423      428       +5     
==========================================
+ Hits          417      419       +2     
- Misses          4        6       +2     
- Partials        2        3       +1     

Flag	Coverage Δ
unittests	97.90% <80.00%> (-0.68%)	⬇️

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[losisin]

closed in favour of #70 and #65