KongStateToFile housekeep + way to improve extensibility

[luccamendonca]

Hey Harry :)

As you may know already, we're working on using decK as a go library to help us with a nice quickstart to manage our Kong EE and offer it as a service to our internal customers.

Starting up has been quick and easy, but we have some specifics here such as wanting to be able to easily dump/sync only data, without necessarily writing or reading files.

Then, we stumbled upon a TODO break-down this giant function on file/writer.go KongStateToFile and we thought about abstracting all the fetching and parsing/zeroing, allowing us to fetch only the data without needing to write the file.

We could do this on our end, of course, but in our opinion it would be something nice to have under decK (or even go-kong itself, which seems to make more sense) to make it a bit more extensible.

What do you think about that, @hbagdi?

Thanks in advance :)

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cc @marcelometal @MayconDionisio