[Extenstions.Enrichment] Update stability status to Beta in README (#3245)

Author: evgenyfedorov2

src/OpenTelemetry.Extensions.Enrichment/README.md

@@ -2,7 +2,7 @@
 
 | Status      |           |
 | ----------- | --------- |
-| Stability   | [Development](../../README.md#development) |
+| Stability   | [Beta](../../README.md#beta) |
 | Code Owners | [@evgenyfedorov2](https://github.com/evgenyfedorov2), [@dariusclay](https://github.com/dariusclay) |
 
 [![NuGet version badge](https://img.shields.io/nuget/v/OpenTelemetry.Extensions.Enrichment)](https://www.nuget.org/packages/OpenTelemetry.Extensions.Enrichment)