Handle BGRA streams in GStreamer backend

[asmorkalov]

Safer replacement for #25557
Jetson Orin provides BGRx stream in some cases.

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• I agree to contribute to the project under Apache 2 License.
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[asmorkalov]

@Liedermaus could you try the patch? I changed format priorities a bit to not break existing behavior.

[asmorkalov]

@opencv-alalek @mshabunin Could you take a look? I fixed regressions and re-order GStreamer caps options.

[mshabunin]

Overall looks good to me.

I'm wondering whether GRAY should be placed before or after Bayer. If we assume this list is sorted in order of required postprocessing, then GRAY should go before Bayer. And if we assume that color image has higher priority, than GRAY should be last.

[asmorkalov]

Color image has higher priority, IMHO.