Allow user to manually specify EPSG for output projection

[scottstanie]

Currently are getting the most common projection from the input SLCs here

dolphin/src/dolphin/stitching.py

Line 186 in ff6e4b0

projection = _get_mode_projection(file_list)

then using that to warp any difference inputs to the same projection before stitching here:

dolphin/src/dolphin/stitching.py

Lines 353 to 357 in ff6e4b0

	to_srs_name = osr.SpatialReference(projection).GetName()
	logger.info(
	f"Reprojecting {fn} from {from_srs_name} to match mode projection"
	f" {to_srs_name}"
	)

This is fine for most cases, but we may want to specify one EPSG for all stitching calls.
If we have a frame which falls on the border of two UTM zones, and there's a chance that a frame with missing data for some dates will get stitched to a different EPSG than the other images.

Additionally, we should do another check before running gdal_merge that the bounds we are passing make sense with the projection, as right now we are assuming that the bounds match the most-common projection