Make add_files to support snapshot_properties argument

[enkidulan]

Issue #694

I'm not sure where to add tests. Is tests/catalog/test_glue.py the right place?

[sungwy]

@enkidulan - thank you for working on this. I think https://github.com/apache/iceberg-python/blob/main/tests/integration/test_add_files.py is the right place for these tests

[enkidulan]

Making params more human-friendly:

test_add_files_to_unpartitioned_table[format_version=1] PASSED
test_add_files_to_unpartitioned_table[format_version=2] PASSED
..
# instead of 
test_add_files_to_unpartitioned_table[1] PASSED
test_add_files_to_unpartitioned_table[2] PASSED

[enkidulan]

Thanks @syun64. I've added the tests

[sungwy]

LGTM. Thank you for adding this in!

[kevinjqliu]

lgtm! love the format_version change

[HonahX]

It looks great! Thanks @enkidulan.

[enkidulan]

I pushed a small update to make Python 3.8 tests pass. I had to replace collections.abc.Iterator with typing.Iterator, as the former only supports subscripting starting with Python 3.9 - https://docs.python.org/3.11/library/typing.html#typing.Iterator.
Sorry that I haven't done that from the start. For some reason, CI only now notified me about the build failing.

[HonahX]

@enkidulan Thanks for fixing the test and the great work! Thanks @syun64 and @kevinjqliu for reviewing. Merging!