WIP plugins: plugin settings on server side

server/controllers/api/index.ts

server/controllers/api/plugins.ts

server/helpers/custom-validators/video-channels.ts

server/initializers/constants.ts

server/lib/plugins/plugin-manager.ts

server/lib/plugins/yarn.ts

server/middlewares/validators/plugins.ts

server/middlewares/validators/sort.ts

server/models/server/plugin.ts

server/typings/express.ts

shared/models/plugins/install-plugin.model.ts

shared/models/plugins/manage-plugin.model.ts

shared/models/plugins/peertube-plugin.model.ts

shared/models/plugins/plugin-library.model.ts

shared/models/plugins/plugin-settings-manager.model.ts

shared/models/plugins/register-hook.model.ts

shared/models/plugins/register-options.model.ts

shared/models/plugins/register-options.type.ts

shared/models/plugins/register-setting.model.ts

shared/models/users/user-right.enum.ts