feat: add new verifyAndParse() method

[wolfy1339]

This method is almost identical to verifyAndReceive(), the difference being that this function won't trigger the event handler, so it can be executed at a later time.

Fixes #379

Resolves #ISSUE_NUMBER

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Before the change?

• Users could not simply get an EmitterWebhookEvent object, the included functions would fire the event handler for webhook events

After the change?

• Users can now get an EmitterWebhookEvent object without the event handler being utilised. This is especially useful for serverless platforms

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

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[github-actions]

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[G-Rath]

wow blast from the past! I'd forgotten about this, which hopefully shows we've all done good work in our code since I do still have lambdas consuming GH events that I've obviously not had to think about in 5 years 😄

I'm not sure though how useful this actually is especially as it doesn't seem like there's been a lot of request for it (but I could easily be wrong there) - looking at my code, I think this would be replacing this custom function:

export const getEvent = async (event: ApiEvent): Promise<GithubEvent> => {
  const rawBody = event.body ?? '{}';
  const signature = event.headers['X-Hub-Signature-256'] ?? '';
  const name = event.headers['X-GitHub-Event'];
  const { GH_WEBHOOK_SECRET } = process.env;

  if ((await verify(GH_WEBHOOK_SECRET, rawBody, signature)) && name) {
    const payload = JSON.parse(rawBody) as GithubEvent['payload'];

    return { name, payload } as GithubEvent;
  }

  throw new Error('event did not come from github');
};

which is pretty small and contained whereas this addition is twice the size - having said that, I'm pretty sure we could easily have verifyAndReceive use this function too which would cut most of the additional size to the package and make it a lot easier to justify