Add SubscriptionsAPI filters to APIServerSource

[rh-hemartin]

This MR adds a page for the experimental feature that add filters to the APIServerSource kind.

Related to #7799 and #7791

Proposed Changes

• Add a page for the experimental feature that adds filters to APIServerSource

[knative-prow[bot]]

Welcome @rh-hemartin! It looks like this is your first PR to knative/docs 🎉

[netlify[bot]]

✅ Deploy Preview for knative ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	f67f0335acb2868f7a086dbcd62460c346ef658c
🔍 Latest deploy log	https://app.netlify.com/sites/knative/deploys/663b72689b5898000844b402
😎 Deploy Preview	https://deploy-preview-5916--knative.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 site configuration.

[pierDipi]

thanks @rh-hemartin, just one comment since we changed it to alpha and disabled

[rh-hemartin]

thanks @rh-hemartin, just one comment since we changed it to alpha and disabled

Thanks for the suggestion, I applied it. This should be squashed when merged?

[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707, pierDipi, rh-hemartin

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~~ [Cali0707]

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