[FEAT] Configure if protected branch rule should apply to admins

- Currently protected branch rules do not apply to admins, however in
some cases (like in the case of Forgejo project) you might also want to
apply these rules to admins to avoid accidental merges.
- Add new option to configure this on a per-rule basis.
- Adds integration tests.
- Resolves #65

models/git/protected_branch.go

@@ -58,6 +58,7 @@ type ProtectedBranch struct {
 	RequireSignedCommits          bool     `xorm:"NOT NULL DEFAULT false"`
 	ProtectedFilePatterns         string   `xorm:"TEXT"`
 	UnprotectedFilePatterns       string   `xorm:"TEXT"`
+	ApplyToAdmins                 bool     `xorm:"NOT NULL DEFAULT false"`
 
 	CreatedUnix timeutil.TimeStamp `xorm:"created"`
 	UpdatedUnix timeutil.TimeStamp `xorm:"updated"`