Add option to output UTC datetimes as "Z" in `.isoformat()`

GitHub fields:

assignee = 'https://github.com/pganssle'
closed_at = None
created_at = <Date 2022-02-02.17:31:46.548>
labels = ['type-feature', 'library', '3.11']
title = 'Add option to output UTC datetimes as "Z" in `.isoformat()`'
updated_at = <Date 2022-04-04.01:30:42.788>
user = 'https://github.com/pganssle'

bugs.python.org fields:

activity = <Date 2022-04-04.01:30:42.788>
actor = 'godlygeek'
assignee = 'p-ganssle'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-02-02.17:31:46.548>
creator = 'p-ganssle'
dependencies = []
files = []
hgrepos = []
issue_num = 46614
keywords = ['patch']
message_count = 6.0
messages = ['412384', '412876', '413102', '416622', '416638', '416648']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'belopolsky', 'eric.araujo', 'p-ganssle', 'godlygeek']
pr_nums = ['32041']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue46614'
versions = ['Python 3.11']