`@remotion/renderer`: Add `--sample-rate` option to control audio output sample rate

Previously, Remotion hardcoded the audio sample rate to 48000 Hz, which caused
quality degradation when source audio had a different sample rate (e.g. 44100 Hz).
This adds a new `--sample-rate` CLI flag and `Config.setSampleRate()` config option
to allow users to specify the desired output sample rate.

Closes #7034

Made-with: Cursor