Lazy load fences

[Adjective-Object]

Adds a config manager to lazy load fences on request

This does not functionally affect a full fence check, it's only useful in partial fence checks. This is for scenarios where we only need to check against a subset of fences (e.g. there are import changes with no fence changes, and we only need to check the fences of the importer and imported files)

[smikula]

I left some minor comments.

[Adjective-Object]

There's no reason .all needs to be a property access as opposed to a getter function so I'm going to update it to getAllConfigs() for consistency.