docs(security): add bug bounty post mortem

[sambacha]

This pull request updates our documentation to include information about a security incident involving a Flashbots relay vulnerability on November 10, 2022. The vulnerability caused block proposers to fall back to local block production due to incorrect timestamp and prev_randao values in block builder submissions. The issue was disclosed by the Manifold team and promptly fixed. Approximately 350 blocks were affected, but no slots were missed.

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