Add metadata.yaml as a requirement (open-telemetry#23340)

Fixes: open-telemetry#20908.

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Co-authored-by: Yang Song <songy23@users.noreply.github.com>

CONTRIBUTING.md

@@ -110,6 +110,7 @@ Components refer to connectors, exporters, extensions, processors, and receivers
 * Implement the [component.Component](https://pkg.go.dev/go.opentelemetry.io/collector/component#Component) interface
 * Provide a configuration structure which defines the configuration of the component
 * Provide the implementation which performs the component operation
+* Have a `metadata.yaml` file and its generated code (using [mdatadgen](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/cmd/mdatagen/README.md)).
 
 Familiarize yourself with the interface of the component that you want to write, and use existing implementations as reference.
 [Building a Trace Receiver](https://opentelemetry.io/docs/collector/trace-receiver/) tutorial provides a detailed example of building a component.
@@ -145,6 +146,7 @@ and the rest of contributors.
 - Add the sponsor for your component and yourself to a new line for your component in the
   [`.github/CODEOWNERS`](./.github/CODEOWNERS) file.
 - Run `make generate-gh-issue-templates` to add your component to the dropdown list in the issue templates.
+- Create a `metadata.yaml` file with at minimum the required fields defined in [metadata-schema.yaml](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/cmd/mdatagen/metadata-schema.yaml) and use the [metadata generator](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/cmd/mdatagen/README.md#using-the-metadata-generator) to generate the associated code/documentation.
 
 When submitting a component to the community, consider breaking it down into separate PRs as follows: