Add Libraries and SDKs section

[defagos]

As a developer I need to know which libraries and SDKs are available, possibly mandatory, recommended or to be avoided.

Acceptance criteria

• The documentation left panel contains a Libraries and SDKs section.
• This section contains a single page per platform, listing SDKs (must, should, could e.g.).
• Platforms are: Web, Android, Apple, Backend, Infra, Data.
• Pages are empty. Dedicated tasks will be done per platform.

Tasks

• [ ] Add documentation section.