Move Collector architecture documentation and diagrams from Github to…

… opentelemetry.io (#4029)

Co-authored-by: Severin Neumann <severin.neumann@altmuehlnet.de>
Co-authored-by: Fabrizio Ferri-Benedetti <fferribenedetti@splunk.com>
Co-authored-by: Juraci Paixão Kröhling <juraci.github@kroehling.de>
Co-authored-by: Phillip Carter <pcarter@fastmail.com>