Merge otel into one file and add package doc (#1176)

No need to split a tiny package into multiple files. Also adding package doc for the otel package.

error_handler.go

@@ -1,22 +0,0 @@
-// Copyright The OpenTelemetry Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package otel
-
-// ErrorHandler handles irremediable events.
-type ErrorHandler interface {
-	// Handle handles any error deemed irremediable by an OpenTelemetry
-	// component.
-	Handle(error)
-}