maint: Update project status and add status link in README (#459)

## Which problem is this PR solving?
Updates project status and add link to sunset issue to README.

## Short description of the changes
- Update project status in `OSSMETADATA` to maintained
- Add link to sunset issue in README
  - #458

OSSMETADATA

@@ -1 +1 @@
-osslifecycle=active
+osslifecycle=maintained

README.md

@@ -4,6 +4,8 @@
 [![CircleCI](https://circleci.com/gh/honeycombio/honeycomb-opentelemetry-java.svg?style=shield)](https://circleci.com/gh/honeycombio/honeycomb-opentelemetry-java)
 [![Maven](https://img.shields.io/maven-central/v/io.honeycomb/honeycomb-opentelemetry-javaagent)](https://mvnrepository.com/artifact/io.honeycomb/honeycomb-opentelemetry-javaagent)
 
+**STATUS**: This project is being Sunset. See [this issue](https://github.com/honeycombio/honeycomb-opentelemetry-java/issues/458) for more details.
+
 This is Honeycomb's distribution of OpenTelemetry for Java.
 It makes getting started with OpenTelemetry and Honeycomb easier!