documentation: Modify outdated developer feature tutorial.

[Rohitth007]

This commit updates the developer-feature-tutorial.md file which used outdated code for the typing feature. Adding to the previous tutorial this add:

• More details about the REST API,
• A complete workflow when using Git,
• A section on setting up dev environment using make,
• Links to Git Guide, Commit Guide and Developer File Overview.

Spellchecks were done through Grammarly and Markdown Linting Rules were introduced and followed.

JSON codeblock converted into YAML as JSON doesn't render nicely in GitHub.

Solves part of #27

[Rohitth007]

Thanks for the suggestions @prah23 . I have made those changes and a corrected few other typos as well.

[Rohitth007]

I have updated all changes requested and cleaned the commits. This is ready to be merged, please take a look. @prah23 @neiljp

[Rohitth007]

@zulipbot add "area: documentation"

[zulipbot]

Heads up @Rohitth007, we just merged some commits that conflict with the changes you made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/main branch and resolve your pull request's merge conflicts accordingly.