[C++] Enable CSV Writer to append / overwrite existing file

This would be a match for the `readr::write_csv()` `append` argument: boolean. If `FALSE` will overwrite existing file. If `TRUE` will append to existing file. In both cases, if the file doesn't exist, a new file is created. 

**Reporter**: [Dragoș Moldovan-Grünfeld](https://issues.apache.org/jira/browse/ARROW-14904) / @dragosmg
#### Related issues:
- [[C++][Python] Un-deprecate FileSystem::OpenAppendStream](https://github.com/apache/arrow/issues/30491) (relates to)

_{**Note**: *This issue was originally created as [ARROW-14904](https://issues.apache.org/jira/browse/ARROW-14904). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start by locating the C++ CSV Writer and read the related issue about un-deprecating FileSystem::OpenAppendStream. The change is complete when the writer can create a missing file, overwrite an existing file when append is false, and append when append is true; verify these behaviors with the relevant C++ tests.

Written by the indexing model from the issue text.