--overwrite-policy enhancements

[geekosaur]

Describe the feature request
--overwrite-policy=upgrade, which should be the new default: automatically overwrites if the package is being replaced by a newer version. (For replacing with the same or an older version, manually specifying --overwrite-policy=always seems reasonable.)
--overwrite-policy=ask, which should probably not be default because of use in CI, unless it can check for stdin being a tty (but is this even meaningful on Windows?).

Additional context
Discussion on #hackage:matrix.org. https://matrix.to/#/%23hackage%3Amatrix.org/%24Y7SP4UGHQ_cN_QVGc-iJYaHwY06tdkPkxx1wIZuHdEY?via=matrix.org&via=kf8nh.com&via=mozilla.org