chore: add emeritus members to working groups

[VerteDinde]

This PR follows up on several off boarding items discussed at the October Boston Electron Summit:

• Adds a status for emeritus, or former members of working groups.
• Adds a description for what qualifies a member for emeritus status
• Explicitly defines a process for removing inactive maintainers from working groups.

This PR does not define what an inactive member means - that definition should be determined individually by each working group, and added to individual working group READMEs.

Note: The members listed here as emeritus were pulled from git and Slack history, and may not be a complete list. If you feel you've been added in error, or are not on the list and should be, please reach out or comment here. 🙏

[dsanders11]

I think we discussed maybe some language around it being a quicker process to return to full member status from emeritus? Not sure if we should add that in charger/README.md.

[erickzhao]

Sorry if we have discussed this elsewhere, but do we want to have emeritus members per WG or just for the project as a whole? Feel like we're gonna get a lot of duplication I guess between WGs.

[dsanders11]

Sorry if we have discussed this elsewhere, but do we want to have emeritus members per WG or just for the project as a whole? Feel like we're gonna get a lot of duplication I guess between WGs.

I kind of like the history that you get when they're per WG - learned a bit of WG history I didn't know. But, this brings up a good point regarding emeritus and defunct WGs - we can't capture those emeritus members since the WG directory no longer exists. So it is probably more complete to do emeritus overall rather than per-WG.