Move important information from build and integration infrastructure documentation

The build and integration infrastructure documentation page mainly
covers a description of how the binary package versioning is formed.
Rework the page to present this information in a slightly more rounded
way and move it to the archtecture section.

We can forgo a list of the services, links to the services should be
provided where they are needed. We need to remove the link to
mattermost history as that is not publically accessible.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>