docs: klip-41: ksqlDB .Net Client (#6613)

Co-authored-by: Alex Basiuk <[email protected]>

design-proposals/README.md

@@ -81,6 +81,6 @@ Next KLIP number: **44**
 | KLIP-37: System Tables                                                                               | Proposal | | | |
 | [KLIP-38: Variable Substitution](klip-38-variable-substitution.md)                                   | Merged         | 0.14.0            | 6.1.0      | [Discussion](https://github.com/confluentinc/ksql/pull/6259) |
 | KLIP-40: Prepared Statements for Java Client                                                         | Proposal | | | |
-| KLIP-41: ksqlDB .NET Client                                                                          | Proposal | | | |
+| [KLIP-41: ksqlDB .NET Client](klip-41-ksqldb-.net-client.md)                                         | Proposal | | | [Discussion](https://github.com/confluentinc/ksql/pull/6613)|
 | KLIP-42: Schema Migrations Tool                                                                      | Proposal | | | |
 | KLIP-43: TIMESTAMP data type support                                                                      | Proposal | | | |

design-proposals/klip-41-ksqldb-.net-client.md

@@ -0,0 +1,72 @@
+# KLIP 41 - ksqlDB .NET Client
+
+**Author**: Alex Basiuk (@alex-basiuk) | 
+**Release Target**: TBD | 
+**Status**: _In Discussion_ | 
+**Discussion**: TBD
+
+**tl;dr:** _Create a ksqlDB client for .NET which is on par with the existing Java client.
+The .NET community will benefit from the this project. The goal is to provide first class developer experience and 
+simplify writing event streaming applications in .NET._
+
+## Motivation and background
+
+Basically, it's similar to [KLIP 15](./klip-15-new-api-and-client.md).
+It should lower the barrier for .NET developers and increase adoption of ksqlDB by the community.
+The library should offer the same feature set as the Java library and should follow common .NET conventions and patterns.  
+
+## What is in scope
+
+* A new client implemented in C#.
+* Initially, the client will be targeted at .NET Core 3 and .NET Framework 5. Support of older versions will be added later.
+* The client will support execution and streaming of queries (both push and pull), inserting of rows into streams, DDL operations and admin operations
+such as list and describe.
+* The client will utilise C# [async streams](https://docs.microsoft.com/en-us/dotnet/csharp/tutorials/generate-consume-asynchronous-stream) feature.
+* The client will also support a direct / synchronous interaction style.
+* High-quality documentation and examples.
+
+## What is not in scope
+
+No plans to provide more functional API for F#. However, it will be possible to use the client in F#.
+
+## Value/Return
+
+Ideas of event sourcing / CQRS / DDD style apps are popular in the .NET community but ksqlDB is often perceived as a Java-specific technology.
+A native client will make it easier to try and hopefully adopt ksqlDB by .NET developers.
+
+## Public APIS
+
+N/A
+
+## Design
+
+* The client will target multiple [target frameworks](https://docs.microsoft.com/en-us/dotnet/standard/frameworks).
+Initially it will be netcoreapp3.0 and net5.0. Support of older versions e.g. netstandard2.0 will be added at later stage.
+* The client will provide an API based on async streams for streaming and async methods for the rest.
+* The client will support injectable [Polly policies](https://github.com/App-vNext/Polly) to enable users to use custom resilience policies. However, out of the box, it should use sensible default retry policies.
+* The client will expose convenience builder extension methods for ASP.NET Core. It should be easy to add and configure the client in ASP.NET Core idiomatic way. 
+  But the mechanism will be optional. Users won't be required to use it or another DI. 
+* The client will have minimal dependencies on third party libraries.
+* The client will follow performance best practices.
+* The client will be thread-safe.
+
+## Test plan
+
+Unit and integration test will be mandatory. Performance benchmarks are desirable but unlikely be the first priority.
+Ideally, tests should be executed on both Windows and Linux platforms.
+
+## LOEs and Delivery Milestones
+TBD
+
+## Documentation Updates
+
+* High quality documentation is required.
+* Example applications showing how to use the client in a real app.
+
+## Compatibility Implications
+
+N/A
+
+## Security Implications
+
+The client will support all protocols supported by the ksqlDB REST API.