[MDEP-608] copy goal should support setting (executable) permissions

**[Julius Schwartzenberg](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=jschwartzenberg)** opened **[MDEP-608](https://issues.apache.org/jira/browse/MDEP-608?redirect=false)** and commented

We have some executables in Nexus as build artifacts. The native plug-in generates those for instance. When we copy them to the target directory so that they can be used with our integration tests, they are not executable however as `chmod +x` is still needed.

It would be nice if the copy goal would support this.

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No further details from [MDEP-608](https://issues.apache.org/jira/browse/MDEP-608?redirect=false)

Start by locating the Maven dependency plugin's copy goal and the tests covering artifact copying. Trace how copied build artifacts receive their permissions, then define the expected behavior for executable artifacts and verify it with the relevant copy-goal tests.

Written by the indexing model from the issue text.