[SCM-924] Enhance SCM changelog model to hold information about tagged commits

**[Sven Linstaedt](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=tzwoenn)** opened **[SCM-924](https://issues.apache.org/jira/browse/SCM-924?redirect=false)** and commented

Hi, in order to support something like semantic releases via maven directly and not some 3rd party tools, not only being able to create tags, but also processing them as part of the changelog would be great.

Tag information are are part of the commit history, accessible via git commandline 

`git log --decorate`

This additional information could be parsed to enhance the ChangeSet model containing optional  information about any tags for this particular commit.

A patch at least for gitexe could be provided, if needed.

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**Affects:** 1.11.2

Start by reading the ChangeSet model and the gitexe implementation, then inspect the output of `git log --decorate` for how tagged commits are represented. The work is done when ChangeSet can optionally retain tag information for a commit and the gitexe path can populate it, with coverage for the parsed history.

Written by the indexing model from the issue text.