Adding/Updating Descriptions for SEO

[fhennig]

Pages should have descriptions with 130 to 150 characters, describing what's on the page. The description gets shown in search results.

• https://github.com/stackabletech/documentation/pull/662
• https://github.com/stackabletech/airflow-operator/pull/503
• https://github.com/stackabletech/druid-operator/pull/620
• https://github.com/stackabletech/demos/pull/97
• https://github.com/stackabletech/hbase-operator/pull/557
• https://github.com/stackabletech/hdfs-operator/pull/580
• https://github.com/stackabletech/hive-operator/pull/511
• https://github.com/stackabletech/kafka-operator/pull/755
• https://github.com/stackabletech/nifi-operator/pull/674
• https://github.com/stackabletech/spark-k8s-operator/pull/463
• https://github.com/stackabletech/superset-operator/pull/538
• https://github.com/stackabletech/trino-operator/pull/641
• https://github.com/stackabletech/zookeeper-operator/pull/856
• https://github.com/stackabletech/opa-operator/pull/624
• https://github.com/stackabletech/commons-operator/pull/279
• https://github.com/stackabletech/secret-operator/pull/499
• https://github.com/stackabletech/listener-operator/pull/223