enhance(admin): show impersonation banner and keep password change with the user (#38924)

Follow-up to https://github.com/go-gitea/gitea/pull/38614

---------

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

services/context/context.go

@@ -228,6 +228,11 @@ func (ctx *Context) DoerNeedTwoFactorAuth() bool {
 	return ctx.Session.Get(session.KeyUserHasTwoFactorAuth) == false
 }
 
+// DoerIsImpersonated returns true if the current session is an admin impersonating the doer
+func (ctx *Context) DoerIsImpersonated() bool {
+	return ctx.Session.Get(session.KeyImpersonatorData) != nil
+}
+
 // HasError returns true if error occurs in form validation.
 // Attention: this function changes ctx.Data and ctx.Flash
 // If HasError is called, then before Redirect, the error message should be stored by ctx.Flash.Error(ctx.GetErrMsg()) again.