How to install missing resampling methods in GDAL Warp (QGIS)?

The method is not in the GUI but you may patch manually the file warp.py as it should be in a path similar to processing/algs/gdal/warp.py

The following code

    def initAlgorithm(self, config=None):
        self.methods = ((self.tr('Nearest Neighbour'), 'near'),
                        (self.tr('Bilinear'), 'bilinear'),
                        (self.tr('Cubic'), 'cubic'),
                        (self.tr('Cubic Spline'), 'cubicspline'),
                        (self.tr('Lanczos Windowed Sinc'), 'lanczos'),
                        (self.tr('Average'), 'average'),
                        (self.tr('Mode'), 'mode'),
                        (self.tr('Maximum'), 'max'),
                        (self.tr('Minimum'), 'min'),
                        (self.tr('Median'), 'med'),
                        (self.tr('First Quartile'), 'q1'),
                        (self.tr('Third Quartile'), 'q3'))

could be changed

    def initAlgorithm(self, config=None):
        self.methods = ((self.tr('Nearest Neighbour'), 'near'),
                        (self.tr('Bilinear'), 'bilinear'),
                        (self.tr('Cubic'), 'cubic'),
                        (self.tr('Cubic Spline'), 'cubicspline'),
                        (self.tr('Lanczos Windowed Sinc'), 'lanczos'),
                        (self.tr('Average'), 'average'),
                        (self.tr('Mode'), 'mode'),
                        (self.tr('Maximum'), 'max'),
                        (self.tr('Minimum'), 'min'),
                        (self.tr('Median'), 'med'),
                        (self.tr('First Quartile'), 'q1'),
                        (self.tr('Third Quartile'), 'q3'))
        if GdalUtils.version() >= 3010000:
            self.methods = list(self.methods)
            self.methods.append((self.tr('Sum'), 'sum'))
            self.methods = tuple(self.methods)

PS: to keep a tuple, I cast it to a list to append Sum method and convert it back to tuple. Quite dirty...

A similar method could be applied for rms sampling method but testing GDAL version to 3.3 and using insert to get the same position in the list as the documentation (https://gdal.org/programs/gdalwarp.html)

If it was a PR, I would also need to look at translation of the new string to be translated maybe.