Add "Safe Mode" issue to Jetpack section

[dylanbaumann]

Re: https://docs.pantheon.io/wordpress-known-issues

Priority: Low

Issue Description

• We should have a section about Jetpack that mentions not activating it fully in pre-production environments.
• We mention it briefly in our WooCommerce guide (which includes Jetpack), but we do not mention it as a standalone issue for the Jetpack plugin, making it hard to discover.

How will this impact users?

• We should have searchable docs for how to remediate this on our site so customers are not surprised by this warning.

Context

• Customer who fully activate Jetpack across multiple environments get a warning that their Jetpack has been put in "Safe Mode" with an ominous screen to either delete their data or override other environments.
• This isn't the only paths forward for solution, they can enable Dev Mode instead for non-Live environments

Suggested Resolution

• Add an "Issue 3" to the Jetpack section which mentions "Safe Mode", and how if you get this warning in pre-production environments you can run them in dev mode instead, similar to how we do on https://docs.pantheon.io/guides/woocommerce/store-setup/

Additional Information

• Example: https://pantheon.zendesk.com/agent/tickets/979176