Add an option to not bail on errors

[gregsidelinger]

Description
#3009 causes external-dns to exit on any errors returned up the stack even though some providers return "soft" errors which do not need to be treated as fatal as they most likely will work on the next controller sync. This change adds a new bail-on-error flag that allows the user to decide how these errors should be treated. The current behavior keeps the current default of exiting on an error however this can be changed to by adding --no-bail-on-error flag.

Fixes #4067

Checklist

• Unit tests updated
• End user documentation updated

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @gregsidelinger. Thanks for your PR.

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[jbilliau-rcd]

Yes please, I heartily endorse this. I can't fathom anybody upgrading past 0.13.4, I still have no idea why this PR was merged or why anybody thought it was a good idea to FATALLY ERROR just because a DNS record can't be created. No other controller I've ever worked with works this way....if this change is going to be kept, at least let us opt out of it and make the controller functional again.

[mloiseleur]

This PR looks good at first glance.
/ok-to-test
/lgtm
@szuecs : Wdyt about settings this option to false by default ?

[szuecs]

@mloiseleur I think the option makes no sense. Why not have errors of type softerror and check with error.Is(), that it's a SoftError?

I can sketch out a PR with it and then everyone can claim that $err is a softerror.

[szuecs]

#4166 adds a feature to add provider.WrapSoftError(err) such that we can differentiate to fail fast or not for a given error. So we will have now the possibility to decide if this is an error that could automatically fix itself or not.