config: space before zone in `default_time_format`'s default

Description

Dates like 2023-10-26 - 23:45CDT look a bit weird, and should be presented as 2023-10-26 - 23:45 CDT. (The default timezone is still UTC, don't worry.)

Checklist

[x] I have read CONTRIBUTING.md
[x] I can and do license this contribution under the EFLv2
[x] No issues are reported by make qa (runs make lint and make test)
- Technically I do get 2 local failures in make test, from the vcrpy problem that #2519 is meant to fix. CI seems to bypass that, so I should be fine. *knocks on wood*
[x] I have tested the functionality of the things this change touches

Notes

While making this, I noticed that Sphinx does not output any of the attribute values. Because of that, we have the same default value defined in three different places. The header line for each attribute ideally would look like a module-level constant, e.g. name_of_config_attribute = ListAttribute('name_of_config_attribute', default=['list', 'of', 'defaults']) (and ListAttribute there would link to the type, of course). It'd save us having to duplicate default values in docstrings, at least.

This patch can't do anything about it, and I couldn't figure out in half an hour of research how to change the docs so Sphinx would do it—but now I'm annoyed, so I wanted to pass that along to everyone else. 🤪

sopel-irc / sopel