refactor: pass CancellationToken to WebhookEventProcessor by default

[JamieMagee]

Follow-up from #708 in preparation for a major version release.

---

Before the change?

• CancellationToken was an opt-in for Octokit.Webhooks.AspNetCore
• It was not possible to pass CancellationToken in Octokit.Webhooks.AzureFunctions

After the change?

• CancellationToken is passed by default in Octokit.Webhooks.AspNetCore and Octokit.Webhooks.AzureFunctions

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

---

[github-actions]

👋 Hi! Thank you for this contribution! Just to let you know, our GitHub SDK team does a round of issue and PR reviews twice a week, every Monday and Friday! We have a process in place for prioritizing and responding to your input. Because you are a part of this community please feel free to comment, add to, or pick up any issues/PRs that are labeled with Status: Up for grabs. You & others like you are the reason all of this works! So thank you & happy coding! 🚀

[sommmen]

LGTM.

I'm not familiar with azure functions, but the CTS is also injected;

CancellationToken

So you could use that straight up instead of getting in from the context, but i would assume they would be the same CTS.