Update docs diagrams to reduce confusion

[davidwrede]

Problem description and possible fixes

Diagrams in the following three locations could use an update:

• How Pulumi Works?

  • Diagram makes it look like we only support javascript -- index.js communicates that

• app.pulumi.com Architecture

  • Diagram is very busy and its not clear whats going on
  • Identity provider list should be updated
  • Should be clear how the Pulumi CLI interacts with both app.pulumi.com and with cloud providers (i.e. metadata for app.pulumi.com and API calls to the cloud provider)
  • Be clear that the blue box represents the context in which the CLI is running (such as a workstation)

• Enterprise Web Architecture

  • Not sure we really need an in-depth diagram about self-hosting options in intro conceptual topic
  • Maybe refactor diagram + self-hosted backend content into dedicated topic(s) on creating a self-hosted backend