GitHub's new auto-help for new contributors labeling

[Fishrock123]

As such, I have renamed good first contribution to good first issue (and updated it to the default color), since this doesn't seem to have configurability. I'll PR docs updates.

Edit: in the case for redirection, we could have good first contribution go to a single issue about it being renamed, though I doubt that will be necessary. If someone looks for it in the labels dropdown this will show up instead.

[Fishrock123]

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