[Headless Recorder] ADD frameskip option to headless recorder

[tgaugry]

This PR add a frameskip option to the headless recorder.
Previous behavior is kept for compatibility.
Frameskip option can have 4 different values :

• noskip and simulationtime : previous behavior, now default. One frame is taken at each time step.
• realtime : Output images at rate of 1/fps
• an arbitrary float : tries to skip this much time between each frame.

The order between simulation and frame saving has also been inverted : now the first frame taken is at time 0, instead of time dt.

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This PR:

• builds with SUCCESS for all platforms on the CI.
• does not generate new warnings.
• does not generate new unit test failures.
• does not generate new scene test failures.
• does not break API compatibility.
• is more than 1 week old (or has fast-merge label).

Reviewers will merge only if all these checks are true.

[damienmarchal]

Rajouter un prefix pour donner l'unité ?
--frameinterval 5.0ms (
--frameinterval 1/60hz (real time)
--frameinterval no (simulation time)

[damienmarchal]

--recordingtime wallclocktime
--recordingtime simulationtime
--recordingtime timeinterval=5ms

Ou
--recordingmode wallclocktime
--recordingmode simulationtime
--recordingmode fixedtimeinterval=5ms

[tgaugry]

Le commit oublié a été rajouté

[hugtalbot]

@tgaugry ok seems good ! could you just (as a final minor remark) add as an explanation on the meaning of the three options RecordMode and their significations: wallclocktime, simulationtime, timeinterval, in HeadlessRecorder.h ligne 67
then we merge !