change: Allow Cypress file watching to be disabled using environment variable

[jdamore-linode]

Description 📝

Allows file watching and automatic reloading to be disabled via an environment variable (including in .env) when using the Cypress UI.

By default, Cypress's UI will automatically reload a test if any changes are made to the spec file which can be disruptive. This PR allows the behavior to optionally be disabled by setting the CY_TEST_DISABLE_FILE_WATCHING environment variable when running Cypress.

Developers can permanently set this behavior by adding it to their .env file.

Major Changes 🔄

• Reads CY_TEST_DISABLE_FILE_WATCHING environment variable to determine whether or not to disable file watching UI
• Adds docs for CY_TEST_DISABLE_FILE_WATCHING

How to test 🧪

1. Run yarn cy:debug
2. Run a test, and modify and save the corresponding test file; observe that Cypress reloads automatically
3. Close Cypress, and run it again with the environment variable: CY_TEST_DISABLE_FILE_WATCHING=1 yarn cy:debug
4. Repeat step 2, confirm that Cypress does not reload automatically

[abailly-akamai]

yessss - thank you 👍 🚢