Improve error handling for invalid JSON in `global_config.json`

[timabbott]

Users who have invalid JSON in their global_config.json file, which is kinda easy to do if you hand-edit JSON and are not good at remembering to skip commas, experience a blank screen when trying to open the application; the only visible errors are in the JS console for the app.

We should introduce a more reasonable user-facing failure here.

[anmolyadav-dev]

@timabbott I am unable to find global_config.json file can you please specify which global_config.json file you are referring to?

[sammamama]

@timabbott I've created a Draft PR. Please let me know any further changes if required.

[Prince-Singh-05]

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