Handle alternative offset formats

[Sharparam]

Currently, you can specify an offset when setting a reminder, e.g.:

/remind 2023-02-14T20:00:00+01:00 Cry in bed because you're alone

However, the other common methods of specifying an offset (+01 for just hours, or +0100 for hours+minutes without a separator) do not work, because Python's "ISO" datetime parser is not ISO compliant.

Perhaps this should be detected and fixed manually within the parsing code in Lonabot? (Like we currently do for converting "Z" and "z" to "+00:00" because Python™.)

I'm prepared to work on this fix but not sure when I will have the time.

[9ary]

Considering python/cpython#80010 is already in python 3.11, I don't think we need to bother fixing this ourselves.