Add support for sha256 repositories (#23894)

Currently only SHA1 repositories are supported by Gitea. This adds
support for alternate SHA256 with the additional aim of easier support
for additional hash types in the future.

Fixes: #13794
Limited by: https://github.com/go-git/go-git/issues/899
Depend on: #28138

<img width="776" alt="图片" src="https://github.com/go-gitea/gitea/assets/81045/5448c9a7-608e-4341-a149-5dd0069c9447">

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

routers/web/repo/repo.go

@@ -159,7 +159,6 @@ func Create(ctx *context.Context) {
 	ctx.Data["private"] = getRepoPrivate(ctx)
 	ctx.Data["IsForcedPrivate"] = setting.Repository.ForcePrivate
 	ctx.Data["default_branch"] = setting.Repository.DefaultBranch
-	ctx.Data["hash_type"] = "sha1"
 
 	ctxUser := checkContextUser(ctx, ctx.FormInt64("org"))
 	if ctx.Written() {
@@ -179,6 +178,8 @@ func Create(ctx *context.Context) {
 
 	ctx.Data["CanCreateRepo"] = ctx.Doer.CanCreateRepo()
 	ctx.Data["MaxCreationLimit"] = ctx.Doer.MaxCreationLimit()
+	ctx.Data["SupportedObjectFormats"] = git.SupportedObjectFormats
+	ctx.Data["DefaultObjectFormat"] = git.Sha1ObjectFormat
 
 	ctx.HTML(http.StatusOK, tplCreate)
 }