Add dice example (#4539)

* Add dice example

* Add manual instrumentation

* Update changelog

* Add comments

* Use naked return consistently

* Move handleFunc to main

* refactor: Extract newHTTPHandler

* Fix comment

* Improve comments

* Update example/dice/otel.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Simplify BaseContext

* Update doc.go

* Update example/dice/main.go

Co-authored-by: Phillip Carter <pcarter@fastmail.com>

* Rename span and metric names

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Phillip Carter <pcarter@fastmail.com>

example/dice/doc.go

@@ -0,0 +1,16 @@
+// 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.
+
+// Dice is the "Roll the dice" getting started example application.
+package main