Update to OpenSearch 1.3.19

It's not clear what changed, but by default gradle is not finding nebula.info-broker when setting up. Adding gradlePluginPortal to the pluginManagement repositories section seems to allow it to work again.

Introduces a very basic release process. No version bumping occurs, the developer must prepare and merge the release then use the trigger_release button to create a tag based on the version number. This may get wrapped up in something more reusable after we have a few examples to work from.

Release triggers do not currently work. afaict it requires trusted runners which are not yet configured for this repo.

Bug: T372769