page_config.json should support json5

[mlucool]

Problem

Similar to overrides, page_config.json should also support json5 so that comments can be added.

Proposed Solution

All json configs should always support json5. Maybe we add a common codepath to enforce this? I.e. instead of doing something like this we refactor this to be reused.

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[peytondmurray]

I'm happy to take this on! Refactoring now to allow json5 everywhere.