make multiline languages configurable

[pfrcks]

• makes .NET optional. Default now is Go, Python and Java
• Customers can override defaults by using stacktrace_languages option in configmap to select the languages they want to use

[pfrcks]

tested scenarios

1. cluster on image with these changes and no configmap -> same as before
2. cluster on image with these changes and old configmap (without stacktrace_languages option) -> same as before all languages enabled
3. cluster on image with these changes and new configmap (one language, multiple languages) -> only specified languages enabled
4. cluster on image with these changes and new configmap (stacktrace_languages = []) -> stacktrace disabled, only cri/docker enabled
5. cluster on image with these changes and new configmap (stacktrace_languages = ["invalid"]) -> stacktrace disabled, only cri/docker enabled