[chore][yamlprovider] Add README file (#12516)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

Add a README for the YAML file with an mdatagen autogenerated section
and basic usage information.

confmap/provider/yamlprovider/README.md

@@ -0,0 +1,26 @@
+# YAML Provider
+
+<!-- status autogenerated section -->
+| Status        |           |
+| ------------- |-----------|
+| Stability     | [stable]  |
+| Distributions | [core], [contrib], [k8s] |
+| Issues        | [![Open issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector?query=is%3Aissue%20is%3Aopen%20label%3Aprovider%2Fyamlprovider%20&label=open&color=orange&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector/issues?q=is%3Aopen+is%3Aissue+label%3Aprovider%2Fyamlprovider) [![Closed issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector?query=is%3Aissue%20is%3Aclosed%20label%3Aprovider%2Fyamlprovider%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector/issues?q=is%3Aclosed+is%3Aissue+label%3Aprovider%2Fyamlprovider) |
+
+[stable]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#stable
+[core]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol
+[contrib]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib
+[k8s]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-k8s
+<!-- end autogenerated section -->
+
+## Overview
+
+The YAML Provider takes a literal YAML string as Collector configuration.
+
+## Usage
+
+The scheme for this provider is `yaml`. Usage looks like the following passed to the Collector's command line invocation:
+
+```text
+--config=yaml:processors::batch::timeout: 2s
+```

confmap/provider/yamlprovider/generated_package_test.go

@@ -1,5 +1,4 @@
-// Copyright The OpenTelemetry Authors
-// SPDX-License-Identifier: Apache-2.0
+// Code generated by mdatagen. DO NOT EDIT.
 
 package yamlprovider
 

confmap/provider/yamlprovider/metadata.yaml

@@ -0,0 +1,8 @@
+type: yaml
+github_project: open-telemetry/opentelemetry-collector
+
+status:
+  class: provider
+  stability:
+    stable: [provider]
+  distributions: [core, contrib, k8s]

confmap/provider/yamlprovider/provider.go

@@ -3,6 +3,8 @@
 
 package yamlprovider // import "go.opentelemetry.io/collector/confmap/provider/yamlprovider"
 
+//go:generate mdatagen metadata.yaml
+
 import (
 	"context"
 	"fmt"