Improve and error handling for update and autoupdate features.

[Jerrie-Aries]

Main issue:

• Fix rare issue with autoupdate feature where the bot raises KeyError while trying to get the commit data. See picture below:
  
  The cause of the issue is probably because of the forked repo name is other than modmail, so the url cannot be found with the response status 404. The response data would be like:

{'message': 'Not Found', 'documentation_url': 'https://docs.github.com/rest/reference/repos#merge-a-branch'} 

Other:

• Add error handling for update and autoupdate features.
• Start autoupdate and post_metadata loops on on_ready event.
• Add read_before_return (type: bool) parameter to GitHub.request method. If set to True, ClientResponse.read() method will be performed first before returning the ClientResponse object. Useful if we want to do other method like .json() or .text() after exiting the ClientSession context manager.
• Fix obsolete references.

[Jerrie-Aries]

I looked at the PR again and just noticed the minor mistake here, the read_before_return should default to False.