Update to Gradle 7 #1505
Description
Is your feature request related to a problem? Please describe.
The OpenSearch Security plugin is still built using Gradle 4.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.
Describe the solution you'd like
Update Gradle to 7.3
Describe alternatives you've considered (Optional)
N/A
Additional context
See please opensearch-project/OpenSearch#1246 and opensearch-project/opensearch-plugins#107