eslint-plugin-patternfly-react - Add support for flat config format for ESLint

[jonkoops]

Currently the eslint-plugin-patternfly-react supports the ESLint v9 plugin API thanks to the work done by @kmcfaul under #10743. However it still requires the use of compatibility functions in order to transform the legacy configuration format to something that can be used in ESLint v9 due to its use of the now required flat configuration format.

The implementation of eslint-plugin-patternfly-react should be updated so it supports the new configuration format, and the documentation in the README should be updated to reflect that. For an example of this, see the documentation for the ESLint markdown plugin.

[github-actions]

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[jonkoops]

This should still be landed in the future, @tlabaj @nicolethoen could this issue be pinned?