Add beam ID to LidarDetection

[ClemensLinnhoff]

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Added beam_id as an identifier to LidarDetection. Now, individual detection points can be assigned to a lidar beam. This enables the identification of multiple returns in one beam and also aligns with the output of some real lidar sensors, e.g. Velodynes.

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[jdsika]

Reviewed for v3.7.0