Add prometheus scrape annotations to RabbitMQ connector

[welteki]

Description

Add Prometheus scrape annotations to RabbitMQ connector to ensure its metrics are scraped by the OpenFaaS Prometheus instance.

Why is this needed?

• I have raised an issue to propose this change (required)

Expose metrics from the RabbitMQ connector.

Who is this for?

What company is this for? Are you listed in the ADOPTERS.md file?

How Has This Been Tested?

Deployed the RabbitMQ connector chart and verified the connector showed up as a Prometheus scrape target.
Verified metrics from the connector are available in Prometheus.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.