docs(DEVELOPER_GUIDE): Make getting started comprehensive and reorgan…

…ize (opensearch-project#3421)

* docs(DEVELOPER_GUIDE): Make getting started comprehensive and reorganize

Enhance getting started guide for new contributors
- Add key technology breakdown with links to code guidelines
- Add robust prerequisite guide
- Clarify forking workflow
- Explain bootstrapping
- Distinguish between recommended and optional/alternative steps
- Add OS-specific guidance
- Add tarball usage instructions

Make other developer guide improvements:
- Update TOC
- Remove callout linking to EUI docs
- Reorder code guidelines
- Standardize header capitalization and make usage guide headers imperative

fixes opensearch-project#3396

Signed-off-by: Josh Romero <rmerqg@amazon.com>

Signed-off-by: Josh Romero <rmerqg@amazon.com>
Co-authored-by: Miki <amoo_miki@yahoo.com>
(cherry picked from commit 5af9a43)

CHANGELOG.md

@@ -58,6 +58,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 - Corrected README and help command of osd-plugin-helpers ([#2810](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2810))
 - Add the release runbook to RELEASING.md ([#2533](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2533))
+- [Doc] Improve DEVELOPER_GUIDE to make first time setup quicker and easier ([#3421](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/3421))
 
 ### 🛠 Maintenance