Upgrade Zulip helm chart to 0.3.0

See !1027 (merged)

We upgraded from 0.2.1 to 0.3.0 in !1027 (merged), but Flux couldn't run the upgrade automatically because some values changed in the upgraded PostgresQL dependency charts. We reverted the Zulip chart version to 0.2.1.

Because the PostgresQL chart dependency basically requires you to re-install the chart, I suspect that if we add the following to the helmrelease, Flux should apply the upgrade correctly, because it will re-install the helm chart.

spec:
  upgrade:
    remediation:
      retries: 1
      strategy: uninstall