Replace "event" with "requests" when they come directly from Slack

[wongjas]

There were some changes made here which replaced the word "event" with "request" when the item in mention came from Slack but these changes were never applied consistenty to the Java docs: slackapi/bolt-js#1013

The page URLs

(List the URLs to update here)

• https://slack.dev/java-slack-sdk/
• (examples in this repository)

Requirements

Please make sure if this topic is specific to this SDK. For general questions/issues about Slack API platform or its server-side, could you submit questions at https://my.slack.com/help/requests/new instead. 🙇

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to the those rules.