update config with plugins found in the default location

[edaniszewski]

Description

plugins can be configured 3 ways:

• via config file (tcp, unix)
• via env (tcp, unix)
• via default socket directory (unix)

the first two options are part of the config search/parse/build flow, so those will be picked up and added to the global config (which one can get from the /config route). the last option, however, is not done through the config flow, so any plugins configured that way will not be added to the global config - thus, we won't see them when we look at the /config route. They will show up for the /plugins route, though.

This issue is to add any plugins found in the default socket dir to the config so someone can see it via the /config route.