New filter: possibility to filter by content type

[htrgouvea]

Context:

Filtering requests by content type (Content-Type) is essential for highlighting relevant responses, especially in applications that return multiple formats (e.g., JSON, HTML, etc.). This feature would be particularly useful when fuzzing applications for specific files or formats.

For example, while searching for package.json files using a custom wordlist and the following parameters:

$ ./nozaki.pl -m GET -u $i -w wordlists/test.txt -r 200 --content "version"

Some false positives still occur. These could be significantly reduced by applying a filter specifically for JSON content types.

What is needed to do:

Add a new option (e.g., --filter-content-type) to allow filtering responses based on the Content-Type header value.
Update the output mechanism to display only the responses that match the filter.
Create tests to validate the feature's behavior and update the README.

Definition of Done:

The --filter-content-type option is functional and supports multiple values.
Tests confirm the filter works as expected.
The feature is documented with examples in the README or equivalent documentation.