Remove HTML rendering from YamlFileConfigurationService

[mikkokar]

Replace YamlFileConfigurationService HTML rendering with yaml or json output format.

Continuation of #605

Rationale:

• Simplifies codebase: A possibility to eliminate an extra library.
• Simplifies codebase: No need to bundle the static assets.
• Eases bug reporting and investigation: Easier for users to send an YAML or JSON file along with bug reports than an HTML page. Also easier for styx core developers to consume it in this format.

Acceptance Criteria:

• Remove assets endpoint from YamlFileConfigurationService.
• OriginsPageRenderer class returns an Yaml or JSON format. Or even better returns whichever format an user agent requested.
• Drop the kotlinx-html-jvm dependency (unless used for something else).