Add support for configuration using Cue

[jamietanna]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

We currently support a number of configuration file formats, i.e. JSON, TOML and YAML.

The Cue configuration language is becoming more widely deployed for configuration, and supports the ability to more strongly

Proposed Solution

Add cuelang.org/go as a dependency, and add support for reading configuration using it.

Alternatives Considered

No response

Additional Information

I'm not sure if this would actually be a good fit, as it may require a stricter format of configuration field types than we currently perform / support.

[github-actions]

👋 Thanks for reporting!

A maintainer will take a look at your issue shortly. 👀

In the meantime: We are working on Viper v2 and we would love to hear your thoughts about what you like or don't like about Viper, so we can improve or fix those issues.

⏰ If you have a couple minutes, please take some time and share your thoughts: https://forms.gle/R6faU74qPRPAzchZ9

📣 If you've already given us your feedback, you can still help by spreading the news,
either by sharing the above link or telling people about this on Twitter:

https://twitter.com/sagikazarmark/status/1306904078967074816

Thank you! ❤️

[sagikazarmark]

There is already a PR implementing a CUE encoder: #1175

The problem is the CUE Go package is quite heavy and I'm reluctant to add it as a dependency.

I'll try to make adding custom encoders easier in one of the next versions so it can become an out-of-tree dependency.