Add multi-tenancy documentation for layered solution template

Author: ahmetfarukulu

docs/en/solution-templates/layered-web-application/images/saas-module-selection.png

@@ -0,0 +1,74 @@
+# Layered Solution: Multi-Tenancy
+
+```json
+//[doc-nav]
+{
+  "Previous": {
+    "Name": "Swagger integration",
+    "Path": "solution-templates/layered-web-application/swagger-integration"
+  },
+  "Next": {
+    "Name": "BLOB storing",
+    "Path": "solution-templates/layered-web-application/blob-storing"
+  }
+}
+```
+
+> Some of the features mentioned in this document may not be available in the free version. We're using the **\*** symbol to indicate that a feature is available in the **[Team](https://abp.io/pricing)** and **[Higher](https://abp.io/pricing)** licenses.
+
+Multi-tenancy is a software architecture where a single instance(codebase) of software runs on a server and serves multiple tenants. Tenants are isolated from each other and can have their own data, configurations, and users. This document explains how the multi-tenancy mechanism works in the layered solution template. You can learn more about multi-tenancy in the [Multi-Tenancy](../../framework/architecture/multi-tenancy/index.md), [Tenant Management](../../modules/tenant-management.md) and [SaaS **\***](../../modules/saas.md) documents.
+
+## Multi-Tenancy in Layered Solutions
+
+The layered solution templates use the *Multi-Tenancy* architecture only if you *Enable Multi-Tenancy **\**** option while creating the solution.
+
+![saas-module-selection](images/saas-module-selection.png)
+
+You can use different databases for each tenant or a shared database for all tenants. In the *SaaS **\*** module, you can specify the database connection strings in the [Connection Strings Management Modal](../../modules/saas.md#connection-string). All cached data is isolated by tenant. Each event, background job, and other data is stored with the tenant id.
+
+You can use the `ICurrentTenant` service to get the current tenant information in your application.
+
+```csharp
+public class MyService : ITransientDependency
+{
+    private readonly ICurrentTenant _currentTenant;
+
+    public MyService(ICurrentTenant currentTenant)
+    {
+        _currentTenant = currentTenant;
+    }
+
+    public void MyMethod()
+    {
+        var tenantId = _currentTenant.Id;
+        var tenantName = _currentTenant.Name;
+    }
+}
+```
+
+Additionally, you can use the [DataFilter](../../framework/infrastructure/data-filtering.md#idatafilter-service-enabledisable-data-filters) system to disable the tenant filter and list all data in the same database.
+
+```csharp
+public class MyBookService : ITransientDependency
+{
+    private readonly IDataFilter<IMultiTenant> _multiTenantFilter;
+    private readonly IRepository<Book, Guid> _bookRepository;
+
+    public MyBookService(
+        IDataFilter<IMultiTenant> multiTenantFilter,
+        IRepository<Book, Guid> bookRepository)
+    {
+        _multiTenantFilter = multiTenantFilter;
+        _bookRepository = bookRepository;
+    }
+
+    public async Task<List<Book>> GetAllBooksIncludingDeletedAsync()
+    {
+        //Temporary disable the IMultiTenant filter
+        using (_multiTenantFilter.Disable())
+        {
+            return await _bookRepository.GetListAsync();
+        }
+    }
+}
+```