Repository: opencv
Issue: The DNN module is missing some layers
Labels: feature,priority: low,category: dnn

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##### System information (version)
<!-- Example
- OpenCV => 4.2
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
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- OpenCV => 4.x
- Operating System / Platform => Ubuntu 18.04.2 LTS
- Compiler => gcc

##### Detailed description

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I used dnn module to evaluate some tensorflow model and I find that dnn has three unimplemented nodes **one_hot**, **maximum** and **minimum**. Could you please help me implement these three layers?

##### Steps to reproduce

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Here is my [models](https://github.com/opencv/opencv/files/7791821/models.zip) and [test files](https://github.com/opencv/opencv/files/7791819/files.zip).
Use command `./test1.o modelPathOfOneHot`, `./test2.o modelPathOfMaximum` or `./test2.o modelPathOfMinimum` to execute.

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