internal/relui: fold SecurityReleaseCoalesceTask into main workflow

The SecurityReleaseCoalesceTask becomes a new
prerequisite step to the minor release workflow;
it keeps all of its prior semantics and execution
flow with minor changes to support idempotent
workflow runs in the larger minor release context.

For golang/go#79034
For golang/go#78458

Change-Id: I76948fa0c8e4d46a0053e14030bd6b36a66e68af
Reviewed-on: https://go-review.googlesource.com/c/build/+/801102
Reviewed-by: Nicholas Husin <nsh@golang.org>
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-by: Neal Patel <nealpatel@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: thatnealpatel

cmd/relui/main.go

@@ -309,6 +309,7 @@ func main() {
 		V3: github.NewClient(githubHTTPClient),
 		V4: githubv4.NewClient(githubHTTPClient),
 	}
+	buildTasks.GitHub = githubClient
 	milestoneTasks := &task.MilestoneTasks{
 		Client:        githubClient,
 		RepoOwner:     "golang",
@@ -416,18 +417,14 @@ func main() {
 		PublicRepoURL: func(repo string) string {
 			return "https://go.googlesource.com/" + repo
 		},
+		GitHub:             githubClient,
 		ApproveAction:      relui.ApproveActionDep(dbPool),
 		SendMail:           mailFunc,
 		AnnounceMailHeader: annMail,
+		AwaitAnnounceMail:  commTasks.AnnounceMailTasks.AwaitAnnounceMail,
 	}
 	dh.RegisterDefinition("Publish a private patch to a x/ repo", privateXPatchTask.NewDefinition(tagTasks))
 
-	securityReleaseCoalesceTask := &task.SecurityReleaseCoalesceTask{
-		PrivateGerrit: privateGerritClient,
-		Version:       versionTasks,
-	}
-	dh.RegisterDefinition("Prepare internal security release branches", securityReleaseCoalesceTask.NewDefinition())
-
 	var base *url.URL
 	if *baseURL != "" {
 		base, err = url.Parse(*baseURL)