Improved webhooks documentation and simulator

We have reviewed and updated our webhook documentation and the webhook simulator data from the account dashboard.

1. Aligned the docs and simulator examples with the actual webhook data fired in production (added missing elements, removed excess elements, aligned data types, corrected lowercase/uppercase values)
2. Used real data instead of some placeholders for the webhook simulator & docs (md5 & sha-1 values, region, bucket name, etc.)
3. Clarified the moment when the video_recorded webhook is sent
4. Clarified that the video_converted webhook is not sent if the mp4 output is disabled in the Transcoding Engine
5. Clarified all the possible values for the type parameter that’s present in many webhooks
6. Removed cutToLength parameter from the video_converted webhook examples and parameters explanations (it does not exist in the actual webhook body)
7. The storedStatus parameter, part of video_copied_pipe_s3 webhook, is now covered in the docs
8. application/json is now the principal webhook type in the docs