Create local-setup-oauth.md

[Dark0d3]

Documentation for oauth in management-api

Description

Added documentation for management api OAuth in local and production

Type of suggestion

• [ ] Typo/grammar fix
• [ ] Updated outdated content
• [x] New content
• [ ] Updates related to a new version
• [ ] Other

Product & version (if relevant)

Umbraco 14+

Deadline (if relevant)