[hold/DNM] allow extensions to provide custom Upstreams

[stevenctl]

Description

We have an extension point for upstreams and endpoints with DiscoveryPlugin, but the EDS emitting logic is based on HybridUpstreamClient. This adds the ability to provide extension there as well.

Code changes

• NewHybridUpstreamClient now takes a list of []plugin.Plugin and adds to the clientMap
• Util function to filter plugins by type using generics
• Replace existing type-filter for DiscoveryPlugin to use helper

Testing steps

WIP enterprise PoC

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[github-actions]

Visit the preview URL for this PR (updated for commit 2523cb8):

https://gloo-edge--pr9901-stevenctl-hybrid-us-br6z6h1p.web.app

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[sam-heilbron]

/kick build-bot never started https://storage.googleapis.com/solo-public-build-logs/logs.html?buildid=ba838d71-ecdb-41ed-9bbd-3f6f1f5d1aa5

[sam-heilbron]

If this error occurs, is that a developer error that we could/should error more loudly about, or is this a case that can occur for some customers?

[stevenctl]

Definitely a dev error. This is called from RunGlooWithExtensions which also bubbles up the error, so I think it's crashing, right?

[stevenctl]

/kick

[stevenctl]

I might not want to merge this after all, some work @lgadban is doing may make it obsolete.

[timflannagan]

@stevenctl is this still relevant based on your last comment or should we close this out?

[stevenctl]

closed in favor of KRT