Expand Run Cadence Tests Guide

[chasefleming]

Expand this running Cadence tests guide to be more comprehensive: https://developers.flow.com/tools/flow-cli/tests/run-tests

• Improve grammar and context in the existing content
• Change the main way to run tests as flow test and have the specific path be a sub option
• Explain testing addresses and flow.json configuration for testing
• Move it into one page in nav, instead of as a single page in the dropdown
• Add missing flags
• Add a better link to the Cadence site syntax docs
• Once finished, link it from the test section of the new Getting Started guide.