Improved and refactored text detection sample in dnn module

[gursimarsingh]

Clean up samples: #25006

This pull requests merges and simplifies different text detection samples in dnn module of opencv in to one file. An option has been provided to choose the detection model from EAST or DB

Pull Request Readiness Checklist

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• [x] I agree to contribute to the project under Apache 2 License.
• [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• [x] The PR is proposed to the proper branch
• [x] There is a reference to the original bug report and related work
• [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable Patch to opencv_extra has the same branch name.
• [x] The feature is well documented and sample code can be built with the project CMake

[asmorkalov]

@gursimarsingh I formatted sample a bit.

[asmorkalov]

Several notes on PR:

• TextDetectionModel section of doc/tutorials/dnn/dnn_text_spotting/dnn_text_spotting.markdown does not correspond to the sample. The command line parameters does not match.
• I propose to add models.yml support to the sample to use download_models.py, and use pre-processing parameters from it. See samples/dnn/object_detection.cpp as example.
• As alternative, we need command line parameters example or / and set default parameters to use samples without parameters.

[gursimarsingh]

@asmorkalov Can you check now?