Generic Forms (#4561)

* Custom Forms

* Update BTCPayServer.Data/Migrations/20230125085242_AddForms.cs

* Cleanups

* Explain public form

* Add store branding

* Add form name to POS form

* add tests

* fix migration

* Minor cleanups

* Code improvements

* Add form validation

Closes #4317.

* Adapt form validation for Bootstrap 5

* update logic for forms

* pr changes

* Minor code cleanup

* Remove unused parameters

* Refactor Form data handling to avoid O(n3) issues

* Rename Hidden to Constant

* Pre-populate FormView from the query string params

* Fix test

---------

Co-authored-by: d11n <mail@dennisreimann.de>
Co-authored-by: nicolas.dorier <nicolas.dorier@gmail.com>

BTCPayServer/Forms/ModifyForm.cs

@@ -8,4 +8,7 @@ public class ModifyForm
 
     [DisplayName("Form configuration (JSON)")]
     public string FormConfig { get; set; }
+    
+    [DisplayName("Allow form for public use")]
+    public bool Public { get; set; }
 }