Proposed changes

Adds a script check-images.sh which can check the agent version and nginx version of all image tags matching a pattern.

Example:

> scripts/check-images.sh agentv3 alpine
Checking images in docker-registry.nginx.com/nginx/agentv3
892 tags fetched.
165 tags after filtering.
tags matching 'alpine': 81
:: docker-registry.nginx.com/nginx/agentv3:1-alpine
nginx version: nginx/1.29.3
nginx-agent version v3.5.0-34a13e6
...

will return all the tags found for the agentv3 image which match the pattern alpine, and run the commands:

• nginx -v
• nginx-agent -v

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13