Format installation errors for GitHub Actions in headless mode

[HebaruSan]

Problem

If metadata pull request validation (see KSP-CKAN/xKAN-meta_testing#61) fails at the installation stage, errors are printed but aren't recognized as errors by the GitHub workflow framework, so they're not highlighted or pinned to the affected file:

• https://github.com/KSP-CKAN/CKAN-meta/runs/1572305201

Cause

Error messages are just passed to IUser.RaiseMessage, despite reporting error conditions, which in turn just outputs via System.Console.WriteLine. GitHub actions require special formatting to recognize error messages.

Changes

• Now one call per error is made to RaiseError, the one that's most likely to be helpful if pinned to a file
• Now if we're in Headless mode, RaiseError prints via log.ErrorFormat, and also replaces all line break sequences with %0A so multi-line messages can be handled properly
• Some other minor cleanup like using DependencyNotSatisfiedKraken.Message since it's nicer than the message we had previously

As far as I could tell we do not have a warning-level message in this code currently, which is good because IUser doesn't have a designated way to handle them.

[DasSkelett]

We should probably do the changes from Cmdline/ConsoleUser.cs to Netkan/ConsoleUser.cs, too.

[HebaruSan]

We can do that, but it looks like all we use that object for is to pass it to KSPManager.

[DasSkelett]

Thanks, let's give it a try!