[whisper] only trigger forced ids warning once

[sanchit-gandhi]

What does this PR do?

Most warnings in generation_whisper.py that are related to config/generation_config parameters are triggered once, e.g.:

transformers/src/transformers/models/whisper/generation_whisper.py

Lines 1128 to 1129 in 1518508

	logger.warning_once(
	"Due to a bug fix in https://github.com/huggingface/transformers/pull/28687 transcription using a multilingual Whisper will default to language detection followed by transcription instead of translation to English."

However, the warnings related to forced_decoder_ids are triggered at every call to .generate. This peppers the stdout and is quite irritating for users to see again and again:

You have passed task=transcribe, but also have set `forced_decoder_ids` to [[1, 50259], [2, 50359], [3, 50363]] which creates a conflict. `forced_decoder_ids` will be ignored in favor of task=transcribe.
You have passed task=transcribe, but also have set `forced_decoder_ids` to [[1, 50259], [2, 50359], [3, 50363]] which creates a conflict. `forced_decoder_ids` will be ignored in favor of task=transcribe.
You have passed task=transcribe, but also have set `forced_decoder_ids` to [[1, 50259], [2, 50359], [3, 50363]] which creates a conflict. `forced_decoder_ids` will be ignored in favor of task=transcribe.
etc.

This PR unifies the logger warnings, to only trigger the forced_decoder_ids warnings once!

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[amyeroberts]

Thanks!