Include test and feature metadata in useragent

[BobyMCbobs]

What would you like to be added:

the useragent should be set per test run to include metadata, specially:

• caller (something like gateway-api-conformance.test)
• gateway-api version
• test name
• features in test

in a parseable format like

gateway-api-conformance.test::v1.1.0::HTTPRouteHTTPSListener::Gateway,HTTPRoute

Why this is needed:

In order to populate gatewaysnoop with information like level (standard, experimental), features per-implementation and version, several metadata values are needed.

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I've made a test implementation version over here
BobyMCbobs@add-useragent-to-conformance-test-run

for example in Kubernetes conformance tests

• https://github.com/kubernetes/kubernetes/blob/2ad04a0505ef13915e11d8b2b3445e514065a9bb/test/e2e/framework/util.go#L527
• https://github.com/kubernetes/kubernetes/blob/272a055/test/e2e/e2e.go#L380