Add in useragent when getting oauth token

[srkirkland]

low priority, but might be nice to add in user-agent when making the oauth request. Shouldn't be required but on 8/2/2024 it became a trigger for the API WAF ruleset, so might be useful in case that's an issue again.

https://github.com/ucdavis/AggieEnterpriseApi/blob/main/src/AggieEnterpriseApi/Authentication/TokenService.cs#L72