Add support for rpm packages

There's [quite a few](https://github.com/repology/repology-updater/tree/master/repos.d/rpm) different public apt package repositories, should at least aim to get centos, fedora and rhel ones indexed.

The docker service has some stats for at least 30,000 packages: https://docker.ecosyste.ms/usage/rpm

## Upvote & Fund

- We're using [Polar.sh](https://polar.sh/ecosyste-ms) so you can upvote and help fund this issue.
- We receive the funding once the issue is completed & confirmed by you.
- Thank you in advance for helping prioritize & fund our backlog.

Start by reviewing the linked repology-updater repos.d/rpm directory and the Docker service's RPM package statistics. Determine how CentOS, Fedora, and RHEL repositories should be represented and indexed, then verify that those repositories and their packages appear in the service's package metadata.

Written by the indexing model from the issue text.