software/theia: Improve additional-frontend logic

Trigger additional-frontend request as soon as any of the relevant
parameters is set by the user:
- additional-frontend-name
- additional-frontend-sr
- additional-frontend-sr-type
- additional-frontend-guid

Instead of only when additional-frontend-guid is set.

software/theia/instance-theia.cfg.jinja.in

+{%- if (parameter_dict.get('additional-frontend-name')
+        or parameter_dict.get('additional-frontend-sr')
+        or parameter_dict.get('additional-frontend-sr-type')
+        or parameter_dict.get('additional-frontend-guid'))%}
+{%- set additional_frontend = true %}
+{%- else %}
+{%- set additional_frontend = false %}
+{%- endif %}
 {%- set parameter_dict = dict(default_parameter_dict, **parameter_dict) %}
-{%- set additional_frontend = parameter_dict['additional-frontend-guid'] %}
 {%- set embedded_instance_config = parameter_dict['initial-embedded-instance'] %}
 
 [buildout]