Package documentation into CMOS

Include a pre-generated set of documentation served by the Nginx web server already running inside CMOS.

CMOS has a landing page that links out to the various components internally along with a reverse-proxy to forward requests to the appropriate components, e.g. /grafana sub-path gets sent to the appropriate port.

The intention here is we provide a packaged offline version of the documentation created during the build process, i.e. we generate HTML from Asciidoc and package it inside the CMOS container. We then serve this documentation via the Nginx web-server as another sub-path. People can therefore run CMOS and get the documentation with it.

The tasks are therefore:

• Add a build target that generates the HTML documentation (this will need the Asciidoc CMOS-51 done).
• Update the container build to package the HTML documentation.
• Update the Nginx configuration to serve the documentation.

The documentation will eventually become part of the official Couchbase documentation on the website but there may always be a need for offline documentation inside the container, plus it is versioned with the source for the container then quite easily which is required for the rapid iteration cycles initially.