ImageWorker.forceComponentColorModel. allow omitting alpha band when going from IndexColorModel to CCM

ImageWorker.forceComponentColorModel allows to expand an IndexColorModel to a ComponentColorModel.
By default, it will include an alpha band if the input colorModel has alpha or if nodata is specified.

It would be great to support a param to omit alpha band creation as part of the color expansion.
That would be useful as an instance when preparing an image for JPEG encoding.
JPEG doesn't support alpha so alpha band will be removed via BandSelect operation right after the color expansion, before the writing operation.
Avoiding to create alpha in advance will optimize the processing (no alpha => no bandSelect required anymore).