Update format for changelog, add developer documentation

Signed-off-by: Kunal Kotwani <[email protected]>

.github/pull_request_template.md

@@ -10,6 +10,7 @@
 - [ ] New functionality has been documented.
   - [ ] New functionality has javadoc added
 - [ ] Commits are signed per the DCO using --signoff 
+- [ ] Commit changes are listed out in CHANGELOG.md file (See: [Changelog](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#changelog))
 
 By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
 For more information on following Developer Certificate of Origin and signing off your commits, please check [here](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#developer-certificate-of-origin).

.github/workflows/changelog_verifier.yml

@@ -1,21 +1,21 @@
 name: "Changelog Verifier"
 on:
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review, labeled, unlabeled]
+    types: [opened, edited, review_requested, synchronize, reopened, ready_for_review, labeled, unlabeled]
 
 jobs:
   # Enforces the update of a changelog file on every pull request
   verify-changelog:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3.0.2
+      - uses: actions/checkout@v3
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
           ref: ${{ github.event.pull_request.head.ref }}
 
       - uses: dangoslen/dependabot-changelog-helper@v1
 
-      - uses: stefanzweifel/git-auto-commit-action@v4.14.1
+      - uses: stefanzweifel/git-auto-commit-action@v4
         with:
           commit_message: "Update changelog"
 

CHANGELOG.md

@@ -3,7 +3,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ## [ UNRELEASED ]
 ### Added
-- Github workflow for changelog verification
+- Github workflow for changelog verification ([#4085](https://github.com/opensearch-project/OpenSearch/pull/4085))
+- Your change here ([#PR_NUMBER](PR_URL))
 
 ### Changed
 

CONTRIBUTING.md

@@ -6,6 +6,7 @@
     - [Documentation Changes](#documentation-changes)
     - [Contributing Code](#contributing-code)
   - [Developer Certificate of Origin](#developer-certificate-of-origin)
+  - [Changelog](#changelog)
   - [Review Process](#review-process)
 
 # Contributing to OpenSearch
@@ -116,6 +117,52 @@ Signed-off-by: Jane Smith <[email protected]>
 ```
 You may type this line on your own when writing your commit messages. However, if your user.name and user.email are set in your git configs, you can use `-s` or `--signoff` to add the `Signed-off-by` line to the end of the commit message.
 
+## Changelog
+
+OpenSearch maintains version specific changelog by enforcing a change to the ongoing [CHANGELOG](CHANGELOG.md) file adhering to the [Keep A Changelog](https://keepachangelog.com/en/1.0.0/) format.
+
+Briefly, the changes are curated by version, with the changes to the main branch added chronologically to `Unreleased` version. Further, each version has corresponding sections which list out the category of the change - `Added`, `Changed`, `Deprecated`, `Removed`, `Fixed`, `Security`.
+
+
+### How to add my changes to CHANGELOG](CHANGELOG.md)?
+
+As a contributor, you must ensure that every pull request has the changes listed out within the corresponding version and appropriate section of [CHANGELOG](CHANGELOG.md) file.
+
+Adding in the change is two step process -
+1. Add your changes to the corresponding section within the CHANGELOG file with dummy pull request information, publish the PR
+
+  `Your change here ([#PR_NUMBER](PR_URL))`
+
+2. Update your changes with the corresponding `PR_NUMBER` and  `PR_URL` and push out the new commit.
+
+For example, as a contributor, my change adds support for a new `FooBar` client, the changes would look like -
+
+```
+# CHANGELOG
+Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
+
+## [ UNRELEASED ]
+### Added
+- ...
+- Add support for FooBar client ([#9999](https://github.com/opensearch-project/OpenSearch/pull/9999))
+- Your change here ([#PR_NUMBER](PR_URL))
+
+### Changed
+- ...
+
+### Deprecated
+- ...
+
+### Removed
+- ...
+
+### Fixed
+- ...
+
+### Security
+- ...
+```
+
 ## Review Process
 
 We deeply appreciate everyone who takes the time to make a contribution. We will review all contributions as quickly as possible. As a reminder, [opening an issue](https://github.com/opensearch-project/OpenSearch/issues/new/choose) discussing your change before you make it is the best way to smooth the PR process. This will prevent a rejection because someone else is already working on the problem, or because the solution is incompatible with the architectural direction.