Added Jenkins file and RELEASING.md (#840)

* Add release workflow jenkins file

Signed-off-by: Owais Kazi <[email protected]>

* Added jenkins file and RELEASING.md

Signed-off-by: Owais Kazi <[email protected]>

---------

Signed-off-by: Owais Kazi <[email protected]>

Author: owaiskazi19

RELEASING.md

@@ -0,0 +1,38 @@
+- [Overview](#overview)
+- [Branching](#branching)
+  - [Release Branching](#release-branching)
+  - [Feature Branches](#feature-branches)
+- [Releasing](#releasing)
+- [Snapshots](#snapshot-builds)
+
+## Overview
+
+This document explains the release strategy for artifacts in this organization.
+
+## Branching
+
+### Release Branching
+
+Given the current major release of 1.0, projects in this organization maintain the following active branches.
+
+* **main**: The next _major_ release. This is the branch where all merges take place and code moves fast.
+* **1.x**: The next _minor_ release. Once a change is merged into `main`, decide whether to backport it to `1.x`.
+
+Label PRs with the next major version label (e.g. `2.0.0`) and merge changes into `main`. Label PRs that you believe need to be backported as `1.x`. Backport PRs by checking out the versioned branch, cherry-pick changes and open a PR against each target backport branch.
+
+### Feature Branches
+
+Do not create branches in the upstream repo, use your fork, for the exception to long-lasting feature branches that require active collaboration from multiple developers. Name feature branches `feature/<name>`. Once the work is merged to `main`, please make sure to delete the feature branch.
+
+## Releasing
+
+The release process is standard across repositories in this org and is run by a release manager volunteering from amongst [maintainers](MAINTAINERS.md).
+
+1. Create a tag, e.g. 1.0.0, and push it to this GitHub repository.
+2. The [release-drafter.yml](.github/workflows/release-drafter.yml) will be automatically kicked off and a draft release will be created.
+3. This draft release triggers the [jenkins release workflow](https://build.ci.opensearch.org/job/opensearch-sdk-java-release) as a result of which the sdk is released on [maven central](https://search.maven.org/search?q=org.opensearch.sdk). Please note that the release workflow is triggered only if created release is in draft state.
+4. Once the above release workflow is successful, the drafted release on GitHub is published automatically.
+5. Increment "version" in [build.gradle](https://github.com/opensearch-project/opensearch-sdk-java/blob/main/build.gradle#L79) to the next iteration, e.g. v1.0.1.
+
+## Snapshot Builds
+The [snapshots builds](https://aws.oss.sonatype.org/content/repositories/snapshots/org/opensearch/sdk/opensearch-sdk-java/) are published to sonatype using [publish-snapshots.yml](./.github/workflows/publish-snapshots.yml) workflow. Each `push` event to the main branch triggers this workflow.

jenkins/release.jenkinsFile

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+lib = library(identifier: '[email protected]', retriever: modernSCM([
+    $class: 'GitSCMSource',
+    remote: 'https://github.com/opensearch-project/opensearch-build-libraries.git',
+]))
+
+standardReleasePipelineWithGenericTrigger(
+    tokenIdCredential: 'jenkins-opensearch-sdk-java-generic-webhook-token',
+    causeString: 'A tag was cut on opensearch-project/opensearch-sdk-java repository causing this workflow to run',
+    downloadReleaseAsset: true,
+    publishRelease: false) {
+        publishToMaven(
+            signingArtifactsPath: "$WORKSPACE/repository/",
+            mavenArtifactsPath: "$WORKSPACE/repository/",
+            autoPublish: false
+        )
+    }