[G-API] Pipeline modeling tool - support local infer node config

[TolyaTalamanov]

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• [ ] I agree to contribute to the project under Apache 2 License.
• [ ] 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
• [ ] The PR is proposed to the proper branch
• [ ] 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.
• [ ] The feature is well documented and sample code can be built with the project CMake

Overview

The motivation of this PR is the following:

1. Some NN models might require individual config
2. Specifying config in .yml config file once is more convenient if it isn't supposed to be changed according user scenario.

The logic is following:

• User can specify configuration parameters for every Infer node locally via .yml config file.
• local config might be combined with global (in case it's specified via --load_config) until they have key conflicts.
• In case "key conflict" app reports the problem and crash.

[TolyaTalamanov]

@smirnov-alexey @dmatveev Hi folks! Could you have a look?

[TolyaTalamanov]

Is everybody OK to merge it?

[TolyaTalamanov]

@alalek @asmorkalov Can it be merged?

[TolyaTalamanov]

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