Add 'allow_maintainer_edit' API option for creating a pull request (#36283)

WebUI has a checkbox for enabling maintainer edits you can check right
away when creating a new pull request.
Also, it is possible to set `allow_maintainer_edit` in an existing pull
request via API.
This change enables the option while creating a new pull request via
API.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/v1/repo/pull.go

@@ -25,6 +25,7 @@ import (
 	"code.gitea.io/gitea/modules/gitrepo"
 	"code.gitea.io/gitea/modules/graceful"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/timeutil"
@@ -496,6 +497,11 @@ func CreatePullRequest(ctx *context.APIContext) {
 		deadlineUnix = timeutil.TimeStamp(form.Deadline.Unix())
 	}
 
+	unitPullRequest, err := ctx.Repo.Repository.GetUnit(ctx, unit.TypePullRequests)
+	if err != nil {
+		ctx.APIErrorInternal(err)
+	}
+
 	prIssue := &issues_model.Issue{
 		RepoID:       repo.ID,
 		Title:        form.Title,
@@ -517,6 +523,8 @@ func CreatePullRequest(ctx *context.APIContext) {
 		Type:       issues_model.PullRequestGitea,
 	}
 
+	pr.AllowMaintainerEdit = optional.FromPtr(form.AllowMaintainerEdit).ValueOrDefault(unitPullRequest.PullRequestsConfig().DefaultAllowMaintainerEdit)
+
 	// Get all assignee IDs
 	assigneeIDs, err := issues_model.MakeIDsFromAPIAssigneesToAdd(ctx, form.Assignee, form.Assignees)
 	if err != nil {