diagram the architecture of the SecureDrop Web applications

[cfm]

Describe the change

We have diagrams of SecureDrop's hardware architecture and data-flow but not the software architecture of the Source and Journalist Interfaces. We should add one (or more), basically peeking into the SecureDrop Application box in https://docs.securedrop.org/en/stable/_images/SecureDrop_DataFlow.png.

How will this impact SecureDrop users?

I spoke with participants at the 2022 Aaron Swartz Day hackathon who appreciated our new repository map but still wanted a diagram of the SecureDrop Web applications in order to understand the codebase more intuitively.