minor refactor to config loading from file/text

[nirrozenbaum]

This PR does minor refactoring to config loading from file/text.
the following changes are included:

• when working with sets, the best practice in k8s is to use "k8s.io/apimachinery/pkg/util/sets", which is backed by map[T]struct{}, but is more readable. updated config loader to use k8s sets.
• config loader doesn't get both text (as bytes) and file anymore. this should be handled in the caller and the config loader gets bytes after the caller converted the file or text into bytes.
  **generally speaking, I'm not sure we need to maintain the two options and using a filepath seems sufficient and more aligned with k8s (e.g., mounting configmap to file system). but this is open for discussion and not part of this PR.
• config loader gets as input the configBytes and the handle to add the plugins. I noticed that LoadConfig and LoadPluginReferences are always called together one after the other, the separation into two functions wasn't making sense.
• updated tests accordingly.

there are more improvements that can be done, e.g., load scheduling profiles with the general config loading. there is no good reason to separate. but this is out of scope of this PR.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nirrozenbaum

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [nirrozenbaum]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[netlify]

✅ Deploy Preview for gateway-api-inference-extension ready!

Name	Link
🔨 Latest commit	190946b
🔍 Latest deploy log	https://app.netlify.com/projects/gateway-api-inference-extension/deploys/686a4f7142132b000819be24
😎 Deploy Preview	https://deploy-preview-1114--gateway-api-inference-extension.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[kfswain]

/lgtm

I noticed the request control plugins are handled separately, is that temporary?

[nirrozenbaum]

/lgtm

I noticed the request control plugins are handled separately, is that temporary?

@kfswain yes, noticed that too. this was the behavior before this PR and I was wondering about it as well.

I think there is room for improvements (the point you raised and few more points), which can be done in follow up PRs.