Provide more information in the Password Protected Posts warning

[benlk]

Is your enhancement related to a problem? Please describe.

https://github.com/10up/10up-experience/blob/14c8794c9c9b34764fa379c45d9112045db03ff4/includes/classes/PostPasswords/PostPasswords.php#L67

It would be nice if this warning changed to suit the context of the site where the plugin is deployed:

• Is there a known-incompatible page-caching layer or host in use? If so, say so
• Is there a known-safe host/cache in use? If so, say so

It would also be nice to link to details of the known insecurity.

Designs

No response

Describe alternatives you've considered

I'm also:

• asking for more advice in Slack
• searching the docs of the host for the site where I'm currently considering enabling this setting

But I figure it would be nice to capture the information and advice in the admin where the setting is, or at least in this repo.

Code of Conduct

• [X] I agree to follow this project's Code of Conduct