Add config file setting that can be used to start butler in minimal mode when API docs should be created

[mountaindude]

When starting with config file setting Butler.restServerApiDocGenerate: true all checking of cert file presence is disabled, all settings except the REST server can (should!) be disabled.

The rationale for this setting is that a minimal feature mode is needed when automatically creating REST API docs.
Butler needs to be started for this to be possible, but when doing this as part of the CI pipeline we don't want any real certificate files or other sensitive settings to be used.