Enhance Application management
Motivation
Currently, we already move the application configuration into FSM, but it sill missed the following gRPCs: register_applicatin, unregister_application, update_application and get_application.
The purpose of this issue is to enhance those gRPC for application management.
register_application was handled in https://github.com/flame-sh/flame/pull/126 .
When unregister_application or update_application, we need to also update Session and Task accordingly. I'm not sure whether we can have them in v0.4.
get_application was fixed in https://github.com/flame-sh/flame/pull/149
unregister_application was fixed in https://github.com/xflops/flame/pull/176
update_application was handled in #182