chore: Bump OpenSearch and OpenSearch Dashboards to 3.4.0

[siegfriedweber]

• OpenSearch and OpenSearch Dashboards versions updated to 3.4.0
• OpenSearch discovery ConfigMap used instead of the hard-coded values
• PUT request to /api/saved_objects/index-pattern/... replaced with POST. PUT should have never worked, except the index pattern was created manually beforehand.
• opensearch-rag: Wait for OpenSearch Dashboards to become ready before creating the index pattern.
• Remove multi-tenancy in OpenSearch because it is not used and selecting the tenant is cumbersome.

Part of stackabletech/docker-images#1379 and stackabletech/docker-images#1380

[razvan]

Everything looks good except for creating the index pattern in the dashboard.

[razvan]

works!