[MNG-8543] Clarify profiles usage

**[Guillaume Nodet](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=gnt)** opened **[MNG-8543](https://issues.apache.org/jira/browse/MNG-8543?redirect=false)** and commented

Profiles are mostly used at built time.

However, there are some use cases for profiles being used at runtime. An example is the `javafx` POM which have a profile used to add a dependency based on the OS name / architecture.

At the same time, file based profiles are also tested when building models for dependencies.  This does not make any sense and should be forbidden.

Properties-based profiles should also be more tightly controlled as leaking properties to the consumed model can lead to unexpected model changes.

The ModelBuilderRequest now has more context, and we do know if we are constructing a built time model or a consumer model (see https://github.com/apache/maven/blob/maven-4.0.0-rc-2/api/maven-api-core/src/main/java/org/apache/maven/api/services/ModelBuilderRequest.java#L59-L71).  So maybe we should restrict a bit more what we do here ?

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No further details from [MNG-8543](https://issues.apache.org/jira/browse/MNG-8543?redirect=false)

Start with api/maven-api-core/src/main/java/org/apache/maven/api/services/ModelBuilderRequest.java, especially the context described at lines 59-71, then trace where profiles are processed during model construction. The issue names no implementation files or tests; done would require agreed rules for build-time versus consumer-model profiles and verification of the resulting behavior.

Written by the indexing model from the issue text.