feat(types): Add gRPC Richer Error Model support (PreconditionFailure) (#1276)

* types: add support for `PreconditionFailure` error message type

Following implementation at flemosr/tonic-richer-error.

* types: doc comments nits

* types: merge `impl` blocks at `std_messages`

tonic-types/src/lib.rs

@@ -46,8 +46,8 @@ pub use pb::Status;
 mod richer_error;
 
 pub use richer_error::{
-    BadRequest, DebugInfo, ErrorDetail, ErrorDetails, ErrorInfo, FieldViolation, QuotaFailure,
-    QuotaViolation, RetryInfo, StatusExt,
+    BadRequest, DebugInfo, ErrorDetail, ErrorDetails, ErrorInfo, FieldViolation,
+    PreconditionFailure, PreconditionViolation, QuotaFailure, QuotaViolation, RetryInfo, StatusExt,
 };
 
 mod sealed {