feat: Mark stable to prepare for 1.0.0 release (#571)

* Release-As: 1.0.0

* Release-As: 1.0.0

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

.repo-metadata.json

@@ -4,7 +4,7 @@
   "product_documentation": "https://cloud.google.com/pubsub/lite/docs",
   "api_description": "Pub/Sub Lite is a zonal, real-time messaging service that lets you send and receive messages between independent applications. You can manually configure the throughput and storage capacity for Pub/Sub Lite systems.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/pubsublite-spark-sql-streaming/latest/history",
-  "release_level": "preview",
+  "release_level": "stable",
   "transport": "grpc",
   "requires_billing": true,
   "language": "java",

README.md

@@ -8,9 +8,6 @@ Java idiomatic client for [Pub/Sub Lite Spark Connector][product-docs].
 - [Product Documentation][product-docs]
 - [Client Library Documentation][javadocs]
 
-> Note: This client is a work-in-progress, and may occasionally
-> make backwards-incompatible changes.
-
 
 ## Quickstart
 
@@ -305,9 +302,6 @@ and on [google-cloud-java][g-c-j].
 This library follows [Semantic Versioning](http://semver.org/).
 
 
-It is currently in major version zero (``0.y.z``), which means that anything may change at any time
-and the public API should not be considered stable.
-
 
 ## Contributing
 
@@ -348,7 +342,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-4]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-pubsublite-spark/java8-win.html
 [kokoro-badge-image-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-pubsublite-spark/java11.svg
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-pubsublite-spark/java11.html
-[stability-image]: https://img.shields.io/badge/stability-preview-yellow
+[stability-image]: https://img.shields.io/badge/stability-stable-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/pubsublite-spark-sql-streaming.svg
 [maven-version-link]: https://search.maven.org/search?q=g:com.google.cloud%20AND%20a:pubsublite-spark-sql-streaming&core=gav
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication