Workflow: Async HTTP and Monitor patterns

[cgillum]

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Description

This PR completes the core content for the workflow patterns document. More specifically:

• The "Async HTTP" pattern is fully populated, including example commands
• The "Monitor" pattern is added, with a description and .NET code sample

Issue reference

Completes most of #3134

/cc @hhunter-ms

[hhunter-ms]

lgtm