improve repo-linter to look for 2 types of OSS readme header images to support dark mode

[jpvajda]

DevEn wanted to make a request to improve repo-linter to look for 2 types of OSS readme header images as the one's it checks for is a version that isn't dark mode friendly. We've been using a better version in our repos lately, but noticed repo linter flags it.

Here is where the ruleset files are and here is an example of where we'd like to see an OR statement looking for both images.

You can see how we are using a darkmode friendly header image in this repo. https://github.com/newrelic/instant-observability-website

[![Community Project header](https://opensource.newrelic.com/static/Community_Project-7c4805883d6396086f907f1c716477cd.png)](https://opensource.newrelic.com/oss-category/#community-project)

We suggest supporting both types as if you change the rule set to darkmode only it would flag a lot of repos which may not have active maintainers to fix them.

[jbeveland27]

Closed by #34