feat: Service discovery and exposition

[siegfriedweber]

Description

Add service discovery and exposition

Changes:

• Service to set up the cluster renamed to <cluster-name>-seed-nodes.
• Discovery service named <cluster-name>, added. The discovery service is used to populate the discovery ConfigMap.
• Discovery ConfigMap named <cluster-name>, added. The ConfigMap contains the keys OPENSEARCH_HOSTNAME, OPENSEARCH_PORT, OPENSEARCH_PROTOCOL and OPENSEARCH_HOSTS. Users should use this information to connect to the cluster.
• Configuration parameter spec.nodes.roleConfig.discoveryServiceListenerClass added to set the ListenerClass for the discovery service.
• Configuration parameter spec.nodes.roleGroups.<role-group-name>.config.discoveryServiceExposed added to expose a role-group via the discovery service.
• Discovery ConfigMap documented

Documentation

https://docs.stackable.tech/home/nightly/opensearch/reference/discovery/

Closes #52

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

• Changes are OpenShift compatible
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible
• Links to generated (nightly) docs added
• Release note snippet added (see Service discovery and exposition #52 (comment))

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added
• Links to generated (nightly) docs added
• Release note snippet added
• Add type/deprecation label & add to the deprecation schedule
• Add type/experimental label & add to the experimental features tracker

[labrenbe]

lgtm