show consumer groups in Topics view

[Dave Shoup (shouples)]

Summary of Changes

Adds consumer groups as a visible resource in the Topics view (pending rename in a future branch):

The Consumer Groups container is shown at the top in a collapsed state, while the Topics container is auto-expanded to be as minimally disruptive as possible for users.

Closes #3300

(Still more work to be done as part of the #3227 parent issue)

Associated PRs

• set up ResourceContainer for Flink database and Kafka cluster child resources #3292
  • show consumer groups in Topics view #3264 👈
    • add commands for consumer groups #3312

Click-testing instructions

1. Connect to a Confluent Cloud environment with an active Kafka cluster
2. Expand the Topics view for that cluster
3. Verify a "Consumer Groups" container appears alongside the "Topics" container
4. Expand the Consumer Groups container and confirm groups are listed with their state (if consumers have been active recently)
5. Expand a consumer group to verify its members (consumers) are shown

Optional: Any additional details or context that should be provided?

• The downstream commands branch (placeholder in the stack) will add context menu actions for consumer groups (e.g., per-container refreshing, reset offsets)
• Consumer group members are fetched per-group using Promise.allSettled, so one failed member fetch won't block the rest

Pull request checklist

Please check if your PR fulfills the following (if applicable):

Tests

• Added new
• Updated existing
• Deleted existing

Release notes

• Does anything in this PR need to be mentioned in the user-facing CHANGELOG?

[sonarqube-confluent]

Quality Gate failed

Failed conditions
76.9% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube