Expose when 'include' is internally injected into CI config content

What does this MR do and why?

This MR addresses the issue described in #391279 (closed). The idea is to pass along a flag contains_internal_include (via pipeline_config) to indicate if the include keyword was dumped into the config content internally, prior to expanding the included files.

The include keyword is currently dumped into the yaml content depending on the config source (ProjectConfig::Source).

MR acceptance checklist

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Related to #391279 (closed)