* support container_component decorator for function with no inputs
* resolve review comments
* add sample tests for milestone 1
* modify compiler test data
* resolve reviews
* resolve reviews
* WIP
* implementation of function of no inputs
* fixed sample test
* re-fix sample test
* fix rebase merge conflict
* resolve formatting
* resolve isort error for test data
* resolve comments
* fix nit
* resolve nit
* add implementation for placeholders i/o, sample and compiler tests
* resolve comments and merge logic for constructing container component
* resolve comments
* resolve comments
* fix assertion messages
* add error handling for accessing artifact by itself
* add test for raising error for accessing artifact by itself
Scott_Xu