Update changelogs from fern repo (#4256)

Co-authored-by: amckinney <5760684+amckinney@users.noreply.github.com>

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2026-03-13.mdx

@@ -0,0 +1,7 @@
+## 2.27.0
+**`(feat):`** Improve gRPC code generation with the following:
+ 1. Updated enum representation and .ToProto + .FromProto mappers.
+ 2. Fix an issue with rendering the gRPC client reference.
+ 3. Update protoc-gen-openapi to unwrap synthetic oneof types (re: https://github.com/fern-api/protoc-gen-openapi/releases/tag/v0.1.7)
+
+