MimeData type for Spectral Profiles

[Benjamin Jakimow]

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• check poossibility to register mime data type for encoded spectral profiles, e.g. 'application/vnd.enmapbox+spectralprofile
• let expression function mime_type(“profile_column”) return a valid mime data type

see:
https://qgis.org/en/site/forusers/visualchangelog320/index.html#feature-mime-type-expression-function
https://en.wikipedia.org/wiki/Media_type
https://datatracker.ietf.org/doc/html/rfc2045