Add recommended/endorsed plugins for addressing site security recommendations

[benlk]

Is your enhancement related to a problem? Please describe.
On https://10up.github.io/Engineering-Best-Practices/site-security/, we recommend several things to do, but we don't say how to do them.

Describe the solution you'd like

We have a list of problems to address. We should add specific methods how to address those problems, such as:

• a line of code to add to wp-config.php
• a filter value to set
• a vetted plugin to install which sets that filter or disables that feature
• a vetted plugin to install which enables or provides that feature
• links to 10up plugins that solve those problems
• links to 10up-maintained public-facing documentation about these issues

Designs

Describe alternatives you've considered

Additional context