Cadence design patterns documentation

[psiemens]

Context

The Cadence design patterns document has been a valuable reference and should be updated to include the latest thinking based on recent smart contract projects.

We also want to add a new "Idiomatic Cadence" document that can act as the start of a Cadence style guide.

Definition of Done

• The Cadence design patterns document includes new design patterns that address common questions and applications that have surfaced within the communtity
• The Idiomatic Cadence document has been created and added to the Cadence section of the documentation site