[Feature]: Allow "end" as alias for the last page

[arnesetzer]

Describe the proposed feature

Analog to pdftk it would be a nice feature if the following syntax would be allowed --pages 3-end when you know, that the first 2 pages are not used.

As far I can tell the changes that need to be done in

OCRmyPDF/src/ocrmypdf/_validation.py

Lines 155 to 191 in 8930efe

	def _pages_from_ranges(ranges: str) -> set[int]:
	pages: list[int] = []
	page_groups = ranges.replace(' ', '').split(',')
	for group in page_groups:
	if not group:
	continue
	try:
	start, end = group.split('-')
	except ValueError:
	pages.append(int(group) - 1)
	else:
	try:
	new_pages = list(range(int(start) - 1, int(end)))
	if not new_pages:
	raise BadArgsError(
	f"invalid page subrange '{start}-{end}'"
	) from None
	pages.extend(new_pages)
	except ValueError:
	raise BadArgsError(f"invalid page subrange '{group}'") from None
	if not pages:
	raise BadArgsError(
	f"The string of page ranges '{ranges}' did not contain any recognizable "
	f"page ranges."
	)
	if not monotonic(pages):
	log.warning(
	"List of pages to process contains duplicate pages, or pages that are "
	"out of order"
	)
	if any(page < 0 for page in pages):
	raise BadArgsError("pages refers to a page number less than 1")
	log.debug("OCRing only these pages: %s", pages)
	return set(pages)

(Need to figure out what the last page of the document is and replace the number with it :D)

Ideas, thoughts on this topic?