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

…ize (#3421) (#3575)

* 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 #3396

Signed-off-by: Josh Romero <[email protected]>

Signed-off-by: Josh Romero <[email protected]>
Co-authored-by: Miki <[email protected]>
(cherry picked from commit 5af9a43)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

# Conflicts:
#	CHANGELOG.md

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>