ci(build): query scorecard image tags with registry v2 api (backport #915)

[mergify]

Welcome to Cryostat! 👋

Before contributing, make sure you have:

• Read the contributing guidelines
• Linked a relevant issue which this PR resolves
• Linked any other relevant issues, PR's, or documentation, if any
• Resolved all conflicts, if any
• Rebased your branch PR on top of the latest upstream main branch
• Attached at least one of the following labels to the PR: [chore, ci, docs, feat, fix, test]
• Signed all commits: git commit -S -m "YOUR_COMMIT_MESSAGE"

---

Fixes: #914

Description of the change:

• Replaced podman search with curl to registry v2 api (quay.io is compatible). References: https://docker-docs.uclv.cu/registry/spec/api/#existing-manifests
• This sends HEAD request to /v2/<name>/manifests/<reference> to check if an image exists for the specified tag.

Motivation for the change:

See #914. I avoided fetching tags since the tag list can grow rather large with time. This method should basically query in constant time and also skip pulling the image layers.

How to manually test:

Check if a image for specified tag exists:

TAG=3.0.1-20240704162318
curl -ILs -o /dev/null https://quay.io/v2/cryostat/cryostat-operator-scorecard/manifests/$TAG -w "%{http_code}"

Sample run: https://github.com/tthvo/cryostat-operator/actions/runs/9884455121/job/27300862066

---

This is an automatic backport of pull request #915 done by [Mergify](https://mergify.com).