Treat warnings as errors across projects

[stijnmoreels]

Is your feature related to a problem? Please describe.
Invalid code XML docs are not being picked up by the build.

What solution would you like?
As a way of picking up invalid XML code docs, we could consider treating warnings as errors across our projects. This way, invalid XML code docs will stop the build.

• Arcus.Security
• Arcus.Messaging
• Arcus.EventGrid
• Arcus.Templates
• Arcus.Observability
• Arcus.BackgroundJobs
• Arcus.WebApi
• Arcus.Testing

Additional context

Discussed in #183

^{Originally posted by fgheysels February 3, 2022}
Should we extend our pipelines so that xml documentation is build / validated ?