Implement ``to-github`` command

[phorcys420]

It would be nice if we could close a discord post and automatically forward it to GitHub.

Notes

We need to avoid allowing mentions to go through in the transcript. We also need to account for escaping the transcript codeblock to input custom markdown, this should work by adding a ZWS to every ` character in the codeblock.

Flow

1. User runs /to-github
2. A GitHub issue is created with the following format
3. The issue link is posted to the channel and pinned
4. The post gets the to-github tag
5. The post gets archived (and locked?)

Issue format

Name : Thread name Content : A post was created in the Discord server and was forwarded to GitHub.

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Conversation transcript

``` [phorcys]: I said this [ben]: I said this ```

Attachements

- [logs.txt](https://cdn.discordapp.com/)

[matifali]

This would be nice to have. Bonus if we can choose between a GitHub issue or a discussion too.

[matifali]

There are 2 ways this can be done,

1. Bot auto creates a GitHub issue.
2. We let the user create the issue where bot just auto fills the Title and Body. https://stackoverflow.com/a/34147022/9183518