Cache github information about the same repository

[holly-cummins]

We're seeing some grey icons for extensions whose URL we definitely know (so we should be able to work out an image). The issue is likely caused by the GitHub rate limiter (despite retries and backing off).

We would ideally cache information between Actions runs (#276), using the Gatsby cache facility and the GitHub actions cache facility, but a simpler solution will get us quite a lot of the way; for repos like camel and quarkus, we don't need to query the repo for each extension that lives in it.

The two exceptions are

• issue counts for quarkus, because we use labels to narrow down the issues to the relevant ones
• extension-specific directory listings (we look for subfolders with the artifact id in the name, to try and find the quarkus-extension.yaml so we can link to it)

Even if we query just issues and the directory listings, that's a savings, because the GitHub rate limiter measures amount of information/complexity of queries, not just the number of queries.

[github-actions]

🙈 The PR is closed and the preview is expired.

[gsmet]

I will trust you on that, feel free to merge when you're happy :). Thanks.