Allow skip_ci to be passed to rebase

Send `skip_ci` flag to Gitaly Rebase RPC and use it as
push options in the PostReceive hook to skip CI.

app/models/repository.rb

@@ -1062,7 +1062,7 @@ class Repository
     rebase_sha
   end
 
-  def rebase(user, merge_request)
+  def rebase(user, merge_request, skip_ci: false)
     if Feature.disabled?(:two_step_rebase, default_enabled: true)
       return rebase_deprecated(user, merge_request)
     end
@@ -1073,7 +1073,8 @@ class Repository
       branch: merge_request.source_branch,
       branch_sha: merge_request.source_branch_sha,
       remote_repository: merge_request.target_project.repository.raw,
-      remote_branch: merge_request.target_branch
+      remote_branch: merge_request.target_branch,
+      skip_ci: skip_ci
     ) do |commit_id|
       merge_request.update!(rebase_commit_sha: commit_id, merge_error: nil)
     end

lib/gitlab/git/repository.rb

@@ -853,7 +853,7 @@ module Gitlab
         end
       end
 
-      def rebase(user, rebase_id, branch:, branch_sha:, remote_repository:, remote_branch:, &block)
+      def rebase(user, rebase_id, branch:, branch_sha:, remote_repository:, remote_branch:, skip_ci: false, &block)
         wrapped_gitaly_errors do
           gitaly_operation_client.rebase(
             user,
@@ -862,6 +862,7 @@ module Gitlab
             branch_sha: branch_sha,
             remote_repository: remote_repository,
             remote_branch: remote_branch,
+            skip_ci: skip_ci,
             &block
           )
         end

lib/gitlab/gitaly_client/operation_service.rb

@@ -233,7 +233,7 @@ module Gitlab
         end
       end
 
-      def rebase(user, rebase_id, branch:, branch_sha:, remote_repository:, remote_branch:)
+      def rebase(user, rebase_id, branch:, branch_sha:, remote_repository:, remote_branch:, skip_ci: false)
         request_enum = QueueEnumerator.new
         rebase_sha = nil