vibrato mark for clavichord

[Bernd Warken]

The clavichord allowed for a special kind of slow vibrato that is not
easy to reproduce on modern pianos.  This vibrato was called "Bebung"
in German baroque scores.  It found it written as a mark above a note
consisting of 5 dots under a slur.  It looks similar to

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I didn't find a suitable mark in lilypond.  Actually, I'm using the
word "vibrato" as a replacement.