Upgrade to Gradle 7

[reta]

Is your feature request related to a problem?
The OpenSearch Plugins are still built using Gradle 6.6.x whereas the Gradle release train has moved to 7.x already. The OpenSearch core is about to be switched to Gradle 7.3 (see please opensearch-project/OpenSearch#1609), it would make sense to switch all plugins to Gradle 7.3 as well.

What solution would you like?
Update Gradle to 7.3

What alternatives have you considered?
N/A

Do you have any additional context?
See please opensearch-project/OpenSearch#1246

• Update to Gradle 7 data-prepper#662
• Update to Gradle 7 alerting#246
• Update to Gradle 7 anomaly-detection#326
• Update to Gradle 7 asynchronous-search#70
• Update to Gradle 7 dashboards-notebooks#105
• Update to Gradle 7 reporting#234
• Update to Gradle 7 index-management#204
• Update to Gradle 7 job-scheduler#104
• Update to Gradle 7 k-NN#230
• Update to Gradle 7 performance-analyzer#92
• Update to Gradle 7 security#1505
• Update to Gradle 7 sql#303
• Update to Gradle 7 observability#278
• Update to Gradle 7 cross-cluster-replication#259
• Update to Gradle 7 common-utils#101