refactor interface page and cache for a day

[codeEmpress1]

Done

• Refactor fetching of interface readme from the repo
• Cache page for a day

  How to QA

• Go to https://charmhub-io-1823.demos.haus/integrations/{interface-name}.json and ensure that a json response is returned as expected e.g https://charmhub-io-1823.demos.haus/integrations/ingress.json
• Got to https://charmhub-io-1823.demos.haus/integrations/{interface-name} and ensure that the page shows as expected e.g https://charmhub-io-1823.demos.haus/integrations/ingress

  Testing

  [ ] No testing required (explain why): This PR is a refactor of the logic and the existing tests still covers it.

Issue / Card https://warthogs.atlassian.net/browse/WD-10963

Fixes #

Screenshots

[webteam-app]

Demo

Jenkins

demos.haus