Allow lower version of python-dateutil in generated client

[bowenwr]

Is your feature request related to a problem? Please describe.

Pretty selfish ask here, but we'd like to consider allowing a wider range of allowed python-dateutil, specifically allowing something below 2.8.1 in the generated client TOML.

Some of our internal tooling which uses both our generated openapi client and aws-sam-cli is incompatible due to a dependency conflict. Specifically, aws-sam-cli requires python-dateutil < 2.8.1. We asked about expanding the acceptable range in aws-sam-cli, since the .1 patch version in particular seems arbitrary and were basically told to pound sand.

I know this is pretty esoteric to our individual use case, but thought I'd ask.

Describe the solution you'd like

Support a more permissive range of python-dateutil under 2.8.1.

Describe alternatives you've considered

We can either make this change in our fork directly - which I was hoping to avoid because I'd like to be able to soon ignore our fork and just use the dependency as is - or continue an internal workaround we have around not using the tooling that causes the dependency conflict.

[dbanty]

I have no problems with that, the only reason for the current version specifier is because that's the version that came up when I added it and the only one I tested with 😁.

Also I read the sam-cli GitHub issue and... that's rough.