docs: cleanup contributors (#28930)

- remove individuals from @angular/* package.json, we don't keep them up-to-date
- switch keys in contributors.json to GitHub handles, seems like a better identifier and lets us grab avatar images from GitHub account
- move emeritus ppl to a new Alumni group (won't yet appear on the site)
- add "lead/mentor" keys so we know who is coordinating work
- add a script that generates an "org chart" graphic

PR Close #28930

aio/scripts/contributors/org_chart.jq

@@ -0,0 +1,11 @@
+# Produces a GraphViz Dot file from the data in the contributors.json file.
+# Documentation for this syntax at https://stedolan.github.io/jq/manual
+to_entries 
+| map(select(.value.group=="Angular" or .value.group=="Collaborator"))
+| map(.value |= {name: .name, lead: (.lead // .mentor // "")})
+| map(
+   "\(.key|tojson) [ label = \(.value.name|tojson) ] ",
+   "\(.key|tojson) -> \(.value.lead|tojson)"
+  )
+[]
+