add an option to allow to generate only models

[codecov[bot]]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (8f164a5) 55.56% compared to head (925fe1f) 55.49%.

:exclamation: Current head 925fe1f differs from pull request most recent head 8eb26ec. Consider uploading reports for the commit 8eb26ec to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #128 +/- ## ========================================== - Coverage 55.56% 55.49% -0.08% ========================================== Files 15 15 Lines 1634 1638 +4 ========================================== + Hits 908 909 +1 - Misses 619 621 +2 - Partials 107 108 +1 ``` | [Files](https://app.codecov.io/gh/omissis/go-jsonschema/pull/128?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Claudio+Beatrice) | Coverage Δ | | |---|---|---| | [pkg/generator/generate.go](https://app.codecov.io/gh/omissis/go-jsonschema/pull/128?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Claudio+Beatrice#diff-cGtnL2dlbmVyYXRvci9nZW5lcmF0ZS5nbw==) | `55.46% <59.52%> (-0.15%)` | :arrow_down: |

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