Bugzilla to GitHub Continued

[Mike Parker]

After [the discussion in the forums regarding the 
migration](https://forum.dlang.org/post/pfpoeaoihsqpohumjvsi@forum.dlang.org), we agreed that Robert would get in touch with GitHub to find out if they could help us post the new GitHub issues under the handles we've mapped to the original contributors on Bugzilla. He learned there's no way to do that directly.

They suggested it might be possible by using an export tool that 
GitLab Enterprise has (yes, GitLab, not GitHub) to get the issues 
from Bugzilla to GitLab, then using GitHub for Business to import 
those issues to GitHub from GitLab. On the surface, that doesn't 
really look feasible. At a minimum, it seems that would require 
every one who submitted a Bugzilla issue to also have a GitLab 
account.

However, he did learn that GitHub has a hidden API we can use 
that will be an improvement on what we have now. Importantly, it 
will allow us to bypass rate limits, making the whole process go 
a lot more quickly. That in turn will allow us to post each 
comment on a Bugzilla issue as a separate comment on the GitHub 
issue.

Our current plan is to go for the latter option. Specifically 
regarding the issues:

* everything will be posted to GitHub under a dummy account
* the Bugzilla handle of the author of each issue will be in the 
GitHub issue's title
* a link to the Bugzilla issue will be added in the initial 
comment
* the author of each issue and everyone on the CC list will have 
their GitHub handles `@` tagged in the initial comment
* each comment on the Bugzilla issue will be posted separately on 
the GitHub issue (I need to verify with Robert that he'll tag the 
GitHub handle of any comment author who isn't already in the CC 
list)
* text from Bugzilla will be posted to GitHub in Markdown code 
blocks to avoid formatting issues
* GitHub labels will be created from Bugzilla keywords and 
applied to the new GitHub issues as appropriate
* the original Bugzilla issue will be updated with a link to the 
new GitHub issue and a note that further comments on the Bugzilla 
issue may not be seen

I think that addresses most of the concerns raised about the 
format of the issues in the previous discussion. Are we missing 
anything?

At some point after the migration, we'll put the Bugzilla 
instance into read-only mode. We've never intended to shut it 
down. We need to migrate it to a server under our control 
eventually. Once it's set to read-only, we'll want dlang-bot to 
still be able to have write access so that it can close issues on 
Bugzilla when the associated issues on GitHub are closed.

Vladimir has already done some preliminary work on dlang-bot. I 
still need to get with him to discuss the process to ensure we 
handle it the right way and are prepared for all of the 
post-migration steps we need to take.