Allow External Plugins to use StandaloneRestTestPlugin gradle plugin

Is your feature request related to a problem? Please describe.
For the k-NN plugin, I wanted to clean up our build.gradle a little bit and pull BWC tests out into a separate subproject. For this, I would like to apply the StandaloneRestTestPlugin or StandaloneTestPlugin as is done for OpenSearch.

However, I am unable to apply the plugin because it adds a project dependency on test-framework, which external plugins do not have access to.

I am wondering if it is possible to modify this so that external plugins can use this gradle plugin? External plugins are able to add dependencies like this:

testImplementation "org.opensearch.test:framework:${opensearch_version}"

Describe the solution you'd like
StandaloneRestTestPlugin can be applied to external plugin build scripts.

Describe alternatives you've considered
Currently, in https://github.com/opensearch-project/k-NN/pull/359, I apply the opensearch build plugin and disable several tasks it adds.

Start with buildSrc/main/groovy/org/opensearch/gradle/test/StandaloneRestTestPlugin.groovy, especially the project dependency described in the issue, and compare its use in qa/full-cluster-restart/build.gradle. Check how an external plugin declares test-framework with testImplementation; done means an external plugin can apply StandaloneRestTestPlugin or StandaloneTestPlugin without lacking that dependency.