convert : handle mmproj filename/path properly (#16760)
* convert: handle mmproj model output filename properly
* remove redundant commits
* Add model_type to gguf utility
* Use mmproj- prefix instead of suffix
* Apply CISC suggestion
Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>
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Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>