[Feature] add selectorConfig endpoint to pds

[xu-hao]

What problem(s) do you aim to solve? having both plugin based and selector based config

What feature solves it and why? add a new endpoint selectorConfig for selector based config.

1. factory default configuration or customized configuration

2. plugin based or selector based

   1. for plugin based: enabled, disabled, or all
   2. for selector based: return all plugins or just default plugin
      1. for return all plugins:
         1. enabled or disabled or all

   pds only returns customized configurations of enabled plugins

What implementation(s) do you suggest? pds: plugin based endpoint: /config return enabled plugins selector based endpoint: /selectorConfig return selector to the default enabled plugin

Anything else? Leave blank, as needed

[xu-hao]

also need to add to pdspi-config