Doc: Create file to track minor ways to customize Plugin Slot

[deborahgu]

There are some ways to customize a Plugin Slot configuration that add further flexibility to how a Plugin Slot renders its contents, and we want to make sure they’re kept track of so any developer can know how they can be used.

h4. Acceptance Criteria:

Create a file in the /docs directory of FPF that points out ways to customize a Plugin or the PluginSlot

• as
• pluginProps
• ready (for iFrame Plugin)
• ErrorFallback (for iFrame Plugin)
• any other nuances