[MNG-8768] Add a function for conditional profile activation evaluating to true if a certain executable can be found in the system path

**[Juan Farré](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=JIRAUSER308727)** opened **[MNG-8768](https://issues.apache.org/jira/browse/MNG-8768?redirect=false)** and commented

I have a use case that I think is of general interest.

I am generating a native image with GraalVM native-maven-plugin, and I'd like to autodetect the presence of the musl gcc compiler wrapper x86_64-linux-musl-gcc in the path to generate a static executable.

When using GraalVM to build an image with the following options,

```bash
native-image --static --libc=musl ...
```

it tries to use x86_64-linux-musl-gcc to compile. If it isn't available in the system path, it crashes.

My idea is to activate a profile when building under Linux x86_64 and the executable x86_64-linux-musl-gcc is detected in the path. This profile would add the options --static and --libc=musl to the native-maven-plugin configuration.

It could be a function like:

```bash
executable(executable_name_or_path)
```

It would search for the executable in the system path (unless a path is given) and check that it's actually an executable.

I think this can be useful for many other use cases.

---

This issue is a sub-task of [MNG-8292](https://issues.apache.org/jira/browse/MNG-8292)

Start by tracing Maven's profile activation mechanism and its existing activation functions; the issue proposes an executable(executable_name_or_path) condition that searches PATH or a supplied path and verifies executability. Use MNG-8768 and parent issue MNG-8292 for context, then add coverage showing profiles activate only when the requested executable is available.

Written by the indexing model from the issue text.