[bitnami/etcd] Add pre-upgrade hook

[pckhoi]

Description of the change

• Add a pre-upgrade hook that removes obsolete members when scaling down the cluster. It runs preupgrade.sh - a new script added in [bitnami/etcd] Stop relying on files for state containers#75906
• Remove pre-stop hook
• Remove removeMemberOnContainerTermination parameter
• Remove initialClusterState parameter

Benefits

Benefits are described more extensively in bitnami/containers#75906 but here are the main points:

• Removing members in pre-upgrade hook is more reliable and with fewer edge cases than in pre-stop hook
• It is far safer to query other members to know whether the cluster is new than to rely on initialClusterState parameter

Possible drawbacks

• If during initialization, the member cannot connect to other members because of a network outage then it will think that it is starting a new cluster. However, I don't think there is any good solution there except manual recovery.

Applicable issues

• fixes [bitnami/etcd] etcd pods are unable to join existing cluster on node drain #16069

Additional information

⚠️ It's needed to cut a new bitnami/common release and use it in this chart, see #31164

Checklist

• Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
• Title of the pull request follows this pattern [bitnami/<name_of_the_chart>] Descriptive title
• All commits signed off and in agreement of Developer Certificate of Origin (DCO)

[carrodher]

Thanks for your contribution!! Just so you know, to run our test suite, separate PRs per chart must be created. In this case, two different PRs are required: one for common and another one for etcd.

[pckhoi]

Sure, I have just created this one: #31164