Support of git push -o options

[giorgioinf]

I would like to recommend a new feature for the release process.

Some git services like gitlab accept git push options to customize their behavior.

I my case, I'd like to skip the gitlab-ci triggering other pipeline during the release process.

Currently it's done via git commit messages, example:

releaseTagComment := s"[ci skip] ${releaseTagComment.value}",
releaseCommitMessage := s"[ci skip] ${releaseCommitMessage.value}",
releaseNextCommitMessage := s"[ci skip] ${releaseNextCommitMessage.value}",

This approach works, but it could be even better without messing up with the commit messages.

As a suggestion:

releasePushCurrentBranchOptions := Seq("ci.skip"), 
releasePushTagsOptions := Seq("ci.skip"),

releasePushOptions := Seq("ci.skip"), # alternative for both above

This would modify the Vcs.scala codes, to something like:

private def pushCurrentBranch = {
    val localBranch = currentBranch
    val options = releasePushCurrentBranchOptions
    cmd(("push" +: options.flatMap(Seq("-o", _)) :+ trackingRemote :+ "%s:%s".format (localBranch, trackingBranch)): _*)
    //cmd("push", trackingRemote, "%s:%s" format (localBranch, trackingBranch))
 }

private def pushTags = {
    val options = releasePushTagsOptions
    cmd(("push" +: options.flatMap(Seq("-o", _)) :+ "--tags" :+ trackingRemote): _*)
    //cmd("push", "--tags", trackingRemote)
}