[MDEP-942] Deprecate the get goal

**[Slawomir Jaranowski](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=slawekjaranowski)** opened **[MDEP-942](https://issues.apache.org/jira/browse/MDEP-942?redirect=false)** and commented

It looks like goal `get` is not usable or can be misunderstood

- there is no `destination` parameter MDEP-395, MDEP-495

But mentioned goal `copy`
- doesn't have a possibility to copy transitive dependencies
- doesn't support additional remote repositories

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**Issue Links:**
- [MDEP-945](https://issues.apache.org/jira/browse/MDEP-945) Fix documentation about get goal

Start by reviewing the Maven Dependency Plugin implementation and documentation for the get and copy goals, then read the linked MDEP-395, MDEP-495, and MDEP-945 issues for context. Done means the get goal is deprecated consistently and its documentation no longer presents it as a usable alternative without addressing the stated limitations.

Written by the indexing model from the issue text.