Design documentation for the SDP MVP

Create initial version of design documentation to compliment the 'getting started guide' (SP-641) targeted towards developers working on the data processing evolutionary prototype.

This should include (but not necessarily be limited to):

• A description of how the different services and controllers work together
• A description of how errors and failures propagate
• A description of how workflows are developed and integrated

This documentation should be maintained alongside the code and be placed under revision control such that it can be easily referred to and and updated as the code evolves.

Where possible, it should be linked (both ways) to the relevant architecture documents so that it provides traceability between the high-level intended architecture and current implemented solution. As the relevant architecture documentation may not yet in a form that supports this traceability, the team developing documentation should stay in close communication with the DP Architect, so that they are up to date with how the SKA Solution Intent is being managed.

As this is a strictly time-boxed activity however, and is expected to evolve in future PIs along with the code, if full traceability to architecture documents is not possible documenting the current implementation should take priority over the practices of SKA Solution Intent.