r.contour
Produces a vector map of specified contours from a raster map. 
Raster (r.*)
QgsProcessingParameterRasterLayer|input|Input raster|None|False
QgsProcessingParameterNumber|step|Increment between contour levels|QgsProcessingParameterNumber.Double|None|True|None|None
QgsProcessingParameterString|levels|List of contour levels|None|False|True
QgsProcessingParameterNumber|minlevel|Minimum contour level|QgsProcessingParameterNumber.Double|None|True|None|None
QgsProcessingParameterNumber|maxlevel|Maximum contour level|QgsProcessingParameterNumber.Double|None|True|None|None
QgsProcessingParameterNumber|cut|Minimum number of points for a contour line (0 -> no limit)|QgsProcessingParameterNumber.Integer|0|True|0|None
QgsProcessingParameterVectorDestination|output|Contours