Added protect namespace to Pydantic v2 ConfigDict

[willarmiros]

In Pydantic v2, a new "feature" was introduced that warned you if your field keys began with model_. However we have several fields that need to be named as such. So per Pydantic docs, this warning can be removed by setting protected_namespaces = () to remove the default protected namespace model_.

This PR allows an extra_data_template JSON file such as the following to be passed into the datamodel-codgen tool and have the protected_namespace change actually take affect. I verified that the warnings disappear on my project after this change.

{
    "MyModelThatIsCausingWarnings": {
        "config": {
            "protected_namespaces": []
        }
    }
}

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e9b6edf) 100.00% compared to head (60a5ddf) 100.00%.
Report is 696 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #1489     +/-   ##
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  Coverage   100.00%   100.00%             
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  Files           11        32     +21     
  Lines         1020      3582   +2562     
  Branches       201       839    +638     
===========================================
+ Hits          1020      3582   +2562     

Flag	Coverage Δ
unittests	99.63% <99.58%> (?)

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Files Changed	Coverage Δ
datamodel_code_generator/__init__.py	100.00% <100.00%> (ø)
datamodel_code_generator/__main__.py	100.00% <100.00%> (ø)
datamodel_code_generator/format.py	100.00% <100.00%> (ø)
datamodel_code_generator/http.py	100.00% <100.00%> (ø)
datamodel_code_generator/imports.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/__init__.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/base.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/dataclass.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/enum.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/imports.py	100.00% <100.00%> (ø)
... and 22 more

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[willarmiros]

It seems there's a missing test line and some typing issues with older Python versions, will try to resolve.

[willarmiros]

@koxudaxi any chance of having this merged?