[Docs]: Implement versioning

[keraron]

Issue Description

Currently the documentation of the various components is not versioned, once we update the docs for SLIM or Directory, the previous versions documentation is gone.

Since these components are being released at different intervals, we need to implement separate versioning for each component.

MkDocs does not support multiple versions under the same website.

Prposed Solution

Split up the documentation, so each component has it's own website that supports versioning.

• docs.agntcy.org would remain as the main page with the Introduction, Getting Started, CSIT, Glossary, and Contributing Guide.
• docs.agntcy would become a landing page with links to navigate to the different components' documentation
• Documentation for OASF, Directory, SLIM, Identity, and Obs/Eval would be moved to <component>.agntcy.org.
• Each components' documentation would live in the component's repo agntcy/<component>/docs
• All sites would have the same style, layout, and configuration.
• Navigation buttons could be added to the header to switch between docs sites.
• use the mike plugin as the versioning tool

Affected Component

Other

Checklist

• I have read the contributing guidelines.
• I have verified this does not duplicate an existing issue.