Define Alternate Steering Group Representative

[zcorpan]

Fixes #223

[annevk]

Chris, Tantek, and I discussed this in meeting. These are my notes based on that:

1. We need to carefully check that everything related to decisions only counts SG Members.
2. We discussed whether these should be like deputy editors or not and the feeling was that "alternate" is correct. I.e., they can stand in for an SG Representative but both are not present at the same time in a decision or meeting. The exceptions to this would be the communication channels such as the shared email address, Slack, and the GitHub team.

Chris and I will also check with our respective organizations to see if there's any further feedback.

[tantek]

I believe this PR now answers all the questions in the comments and in the meetings.

[diekus]

lgtm

[annevk]

Simon did not actually commit the proposed change to the PR. I'm guessing everyone agreed to the PR under the assumption that change is incorporated? It looks okay to me.

[annevk]

This looks good, but we should make sure to get feedback on "Qualified Voting Party" in https://whatwg.org/sg-agreement#5-definitions first.

[tantek]

See latest suggested revision from @zcorpan: https://github.com/whatwg/sg/pull/235/files#r1931061498

This LGTM with that edit.

[zcorpan]

I've updated the PR to incorporate @annevk's suggested changes.