NGINX plus receiver

[dhurley]

Proposed changes

• Collect NGINX Plus metrics
• Update collector configuration to be dynamic depending on want instances are found
• Add build agent with nginx plus image make target
• Add mock OTel collector package for testing purposes

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