Azure.Sdk.Tools.GithubCodeownerSubscriber_1.0.0-dev.20221129.1

Create a missing .sln file for notification-configuration tool (#4821)

This PR makes it easy to open in Visual Studio the `.csproj` files that are descendants of `tools/notification-configuration` path, by adding a `.sln` file containing minimum set of projects required to do a successful build.

I created the `.sln` file by doing the following in VS:
- new project -> blank solution; named it `notification-configuration` and placed in the dir `tools\notification-configuration`
- added `tools\notification-configuration\github-codeowner-subscriber\Azure.Sdk.Tools.GithubCodeownerSubscriber.csproj`  
- added `tools\notification-configuration\notification-creator\Azure.Sdk.Tools.NotificationConfiguration.csproj`
- added the two other required projects to make the build succeed;
- added `ci.yml` as solution file.

I also deleted `ci.proj` to avoid the `MSBUILD : error MSB1011: Specify which project or solution file to use because this folder contains more than one project or solution file.` error.