[chore][receiver/splunkenterprise] Add header to README (#32956)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
The readme for the Splunk Enterprise receiver does not currently have
the autogenerated header. This was missing because `mdatagen` requires
`<!-- status autogenerated section -->` and `<!-- end autogenerated
section -->` to know where to insert the generated data.

receiver/splunkenterprisereceiver/README.md

@@ -1,5 +1,16 @@
 # Splunk Enterprise Receiver
 
+<!-- status autogenerated section -->
+| Status        |           |
+| ------------- |-----------|
+| Stability     | [development]: metrics   |
+| Distributions | [] |
+| Issues        | [![Open issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector-contrib?query=is%3Aissue%20is%3Aopen%20label%3Areceiver%2Fsplunkenterprise%20&label=open&color=orange&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues?q=is%3Aopen+is%3Aissue+label%3Areceiver%2Fsplunkenterprise) [![Closed issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector-contrib?query=is%3Aissue%20is%3Aclosed%20label%3Areceiver%2Fsplunkenterprise%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues?q=is%3Aclosed+is%3Aissue+label%3Areceiver%2Fsplunkenterprise) |
+| [Code Owners](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CONTRIBUTING.md#becoming-a-code-owner)    | [@shalper2](https://www.github.com/shalper2), [@MovieStoreGuy](https://www.github.com/MovieStoreGuy), [@greatestusername](https://www.github.com/greatestusername) |
+
+[development]: https://github.com/open-telemetry/opentelemetry-collector#development
+<!-- end autogenerated section -->
+
 The Splunk Enterprise Receiver is a pull based tool which enables the ingestion of performance metrics describing the operational status of a user's Splunk Enterprise deployment to an appropriate observability tool.
 It is designed to leverage several different data sources to gather these metrics including the [introspection api endpoint](https://docs.splunk.com/Documentation/Splunk/9.1.1/RESTREF/RESTintrospect) and serializing
 results from ad-hoc searches. Because of this, care must be taken by users when enabling metrics as running searches can effect your Splunk Enterprise Deployment and introspection may fail to report for Splunk