bump: update OpenCV version to 4.13.0

[Borda]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

This pull request updates the OpenCV version used across the project from 4.12.0 to 4.13.0. The change is reflected in the Docker build configurations, documentation, and both CPU and GPU Dockerfiles to ensure consistency and compatibility with the latest OpenCV release.

OpenCV version upgrade:

• Updated the default OPENCV_VERSION argument from 4.12.0 to 4.13.0 in both cpu/Dockerfile and gpu/Dockerfile to use the latest OpenCV version. [1] [2]
• Modified the build matrix in .github/workflows/docker-builds.yml to use opencv_version: ["4.13.0"] and updated all explicit matrix entries for Ubuntu 24.04 to reference OpenCV 4.13.0.

Documentation update:

• Updated the OpenCV version mentioned in the image tag descriptions in README.md from 4.12.x to 4.13.x for both CPU and GPU builds.

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

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