feat: added custom error handler function

[alexraileanu]

Sometimes I want to manually define a way that an error is presented to the user (for instance to change color output and such). This PR adds a way to do so via the new SetErrorHandlerFunc method

[CLAassistant]

All committers have signed the CLA.

[jpmcb]

Hmmm interesting.

The code looks good, but I want to understand what this is trying to solve.

Can you provide a sample cobra program where something like this would be useful? Seems like you'd want to set this per command to handle different errors from different commands differently?

[alexraileanu]

@jpmcb thanks for your feedback. i created a gist where i can show you an example where this feature would be useful: https://gist.github.com/alexraileanu/200a4473653efa8fbda6e555bd3fc428.

in the screenshot below, you can see that my custom error handlers have different colored messages, however the Error: prefix is added to both. my code, provides a way to give the developer full control over what is output to the user in case of an error.

please let me know if you need any more clarification as i would really like to make use of this feature :)

[alexraileanu]

@jpmcb @marckhouzam kindly requesting a review of this as i'd very much like to have this feature in my project

[alexraileanu]

@jpmcb sorry for the mess, i did some mistakes on my side of github but it looks like it's all good now.

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[marckhouzam]

As we have very few maintainers, and those have very little time, we've decided to remove the auto-close configuration.
I'm re-opening this PR since it was closed automatically.