Readme backend cache is not configurable and therefore caches indefinitely

[stuartsaid]

Describe the feature

Allow the user to provide a TTL for the CacheService within the readme-backend plugin and utilise a sensible default value

At present as no ttl value is provided when setting the readme contents in the cache it is cached indefinitely. This then means that in order to see updates to the readme the instance of Backstage has to be restarted. I suggest that we:

• Set a sensible default for the ttl of say an hour (happy to discuss or use another default)
• Allow the user to optionally configure this in the app-config under a new readme.cacheTTL key, otherwise use the default

Added value

Users will be able to see updates (while retaining the benefits of a cache) to the README without having to restart their running backstage instance, which is not very practical to do for every readme update.

Additional context

I'm more than happy to submit a PR for this, I believe it should be a pretty straightforward change - raising a github issue as per the contributing guidelines!

[anicke]

Sounds good! A PR would be appreciated. 👍

[stuartsaid]

I've attempted to push up to a new branch, however I'm getting a 403 error with permission denied. Do you need to do anything to allow me to push @anicke?

[anicke]

The normal workflow is to create a fork and create a PR from the that fork.