Fix: empty property value is considered as "not set" by quarkus

[Ksiona]

Redesigned:

• The code contains a property, but no corresponding environment variable.
• This property must be mapped to an environment variable, serving as its default value in the configuration file (to docs)
• The property accepts a comma-separated list of allowed values; specifically, it should be populated with headers from the internal blacklist (which is not externally configurable). The property name is quarkus.context.propagation.allow-blocked-headers, and it is case-insensitive.
• The documentation must clearly explain—from start to finish—how to configure this property in application.yaml using an environment variable. We handle this up to the container's environment variable level.