Implement the Mulibuffer Point Function

[mvmaltitz]

We need a function that generates buffers from a point at different increment buffer distances.

##Signature:
Grid(bbox, country_boundary, cellsize, output_path, crs, increment_values, input_point_layer)

##Inputs:
bbox - the grid aligned bounding box for the analysis area. e.g. if the grid size is 100m the length and width will be exactly divisible by 100m
country_boundary - a QgsVectorLayer of type polygon or multipart polygon. Areas outside of this boundary will be assigned nodata.
output_path - the place in the filesystem where the dataset should be written. ⚠️ If it already exists it will be overwritten without confirmation.
crs - typically a UTM zone for the analysis area. Should be m based.
cellsize - based on the analysis environment, typically 100m
increment_values - based on user input, these are the values that are going to be used to create the buffer. Maximum number of increment values = 5. The default should be 250, 500, 750, 1000, 1250
input_point_layer - the input point layer will be the center points of the buffer

##Outputs:
a QgsRasterLayer
The analysis will generate a new raster layer in the input CRS and dimensions of the input bbox and cell size. It will be assigned a value between 0 and 5. All values outside of the country_boundary will be assigned as no data values.
The suggested thresholds should be adjusted to:
0 to 250 meters: 5
251 to 500 meters: 4
501 to 750 meters: 3
751 to 1,000 meters: 2
1,001 to 1,250 meters: 1
Over 1,250 meters: 0

##Testing:
Prepare a small sample dataset for the boundary and verify that the buffer generates correctly