G-API OV backend requires partial shape support

[DariaMityagina]

Pull Request Readiness Checklist

Addressing the TODO from G-API OV backend requires cv::MediaFrame PR

• [x] As part of the review process this comment was addressed which make it impossible to run the demo. I will bring those changes back in a separate PR [support PartialShape]

Background_subtraction demo G-API issue: Porting to API20 resulted in an error (both for CPU and NPU):

[ERROR] OpenCV(4.9.0-dev) /home/runner/work/open_model_zoo/open_model_zoo/cache/opencv/modules/gapi/src/backends/ov/govbackend.cpp:813: error: (-215: assertion not done ) cv::util::holds_alternative<cv::GMatDesc>(input_meta) in function 'cfgPreProcessing'

Adding cv::MediaFrame and partial shape support to govbackend resulted in the following (tested with CPU):

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

• [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.
• [ ] The feature is well documented and sample code can be built with the project CMake

[asmorkalov]

@dmatveev @TolyaTalamanov Friendly reminder.