[Proposal] Add a deprecation warning for `render_interval`'s predecessor `SimulationCfg.decimation`

[jsmith-bdai]

Proposal

Add in a deprecation warning when a user tries to set sim_cfg.decimation. Also update migration guide to explain the update to the parameter.

Motivation

Recently render_interval was introduced as a way of handling the # of frames between rendering. Previously this was handle via sim_cfg.decimation. For users using the old parameter, rendering will occur each physics step which likely causes a big performance hit.

Checklist

• [x] I have checked that there is no similar issue in the repo (required)

Acceptance Criteria

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• [ ] Deprecation warning added for SimulationCfg.decimation
• [ ] Isaac Lab migration guide from Orbit updated to include new parameter