Allow users to add s3 tags when they pin_write

See https://github.com/rstudio/pins-r/issues/628.

Note that pins passes through extra keywords in pin_write to its S3 API library:

board_sales <- board_s3("company-pins", prefix = "sales/")
board_sales %>% pin_write(mtcars, Tagging = "key1=value1&key2=value2")

Here is how s3fs tests tagging:

# from the s3fs tests
def test_tags(s3):
    tagset = {'tag1': 'value1', 'tag2': 'value2'}
    fname = list(files)[0]
    s3.touch(fname)
    s3.put_tags(fname, tagset)
    assert s3.get_tags(fname) == tagset

Start by tracing the Python implementation of pin_write and how it forwards extra keywords to the S3 API library. Review the linked pins-r issue and the s3fs tagging test for the expected tag format and behavior. Done means callers can supply Tagging through pin_write and coverage verifies the tags are applied.