Fix zulip group zulip-id availability check

[jieyouxu]

The previous validate_zulip_group_ids check logic is not quite correct in two ways:

1. The previous logic was too strict, in that it does not properly account for the case where a team member may not be included in any team-associated zulip user groups (such as via the excluded-people mechanism).
2. The previous logic I think was also too loose, in that it is possible to attach additional extra people via extra-people. It is possible to include a person whose people/ entry contain only a github handle, and not also a zulip id.

Example

Consider the cloud-compute marker-team:

name = "cloud-compute"
kind = "marker-team"

[people]
leads = []
members = [
   "have_zulip_id",
   "no_zulip_id",
]

[[zulip-groups]]
name = "cloud-compute"
extra-people = [
   "extra_no_zulip_id",
]
excluded-people = [
   "no_zulip_id",
]

The "all zulip group members must have a zulip-id" validation should fail, but not against no_zulip_id, because that member is not part of any zulip groups associated with cloud-compute team. It should error on extra_no_zulip_id however.

Review remarks

Let me know if these validations have any tests... I can't figure out if the static-api tests are intended for this purpose, I don't think so. I tested these two cases manually, and the revised logic seems to behave as I would expect it to.

[jieyouxu]

Context: the zulip groups I was trying to create for infra announcement channel.

cf. #t-infra > Communication method for dev desktops @ 💬

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing github
[INFO  sync_team] 💻 Team Diffs:
    📝 Editing team 'rust-lang/all':
      Adding member 'graciegregory' with member role
    📝 Editing team 'rust-lang/community-survey':
      Adding member 'graciegregory' with member role
    📝 Editing team 'rust-lang/wg-triage':
      Adding member 'edmilsonefs' with member role

[marcoieni]

Does the old logic require that all members of teams have a zulip id? If yes, are we loosing this property with this change?