Migrate to AsciiDoc

All documentation needs to be moved over to Asciidoc.

This means translating the Markdown documentation currently in the CMOS repository: https://github.com/couchbaselabs/observability/blob/main/README.md 

There is also some documentation in the cluster monitor that needs migrating over to the CMOS repository but this is lower priority: https://github.com/couchbaselabs/cbmultimanager/blob/master/README.md and https://github.com/couchbaselabs/cbmultimanager/tree/master/doc

A separate docs directory at the top-level should be set up for all this with some linkage then down from the landing page of the repository in Github, i.e. when people browse to this on the web they can see the documentation rendered correctly.

This needs to follow the standard Couchbase approach to allow us to integrate it later into the website. Initially we will be generating this documentation offline to include directly in the container though. The goal here is to provide documentation as if it would be published on the Couchbase website ready for simple inclusion later.

Contribution guidelines should be provided, the intention is to encourage external contribution so we need to tell people how to do this.

Documentation linting should also be provided as part of the makefile, similar to other Couchbase products like the operator. This will also help with contribution and CICD actions. Keeping the documentation all within the docs directory will help target the jobs to run on changes as well.